TSB Final Report Summaries

The following summaries are extracted from final reports issued by the Transportation Safety Board of Canada (TSB). They have been de-identified and include the TSB’s synopsis and selected findings. Some excerpts from the analysis section may be included, where needed, to better understand the findings. For the benefit of our readers, all the occurrence titles below are now hyperlinked to the full TSB report on the TSB Web site. —Ed.

TSB Final Report A10A0041—Loss of Control and Collision with Terrain

On April 23, 2010, a Grumman TBM-3E fire-fighting aircraft departed Miramichi Airport, N.B., for a practice water drop flight at about 13:38 ADT. Approximately 2 min later, the aircraft collided with terrain just south of the airport. Emergency responders and workers from nearby businesses responded immediately. The aircraft was destroyed by the impact forces. There was no reported emergency locator transmitter signal. Medical examination determined that the pilot had suffered a heart attack prior to the aircraft impacting the ground. The TSB authorized the release of this report on July 4, 2011.

Photo 1 TBM fire-fighting aircraft
TBM firefighting aircraft

Analysis

Nothing was found to indicate that there was any airframe failure or system malfunction prior to or during the flight. It was also determined that the weather conditions did not play a role in this occurrence. The autopsy determined that the pilot had suffered a heart attack, resulting in the aircraft departing controlled flight and the impact with the ground. Therefore, the analysis will focus on the medical aspects of the investigation.

The pilot's medical status was being followed by a family physician who originally diagnosed the pilot with hypertension in 1998. The pilot was taking medication to treat this condition. However, this information was not recorded on the Canadian Aviation Medical Examination Report (CAMER) until 2008 because the pilot had not disclosed this information to the Civil Aviation Medical Examiner (CAME) and the family physician had not reported the relevant condition to Transport Canada (TC). Present regulations provide the CAME with the authority and the means to obtain any additional medical information necessary to determine if a pilot meets the medical requirements of their licence. However, if there is no basis to do so because a pilot has not disclosed a symptom/condition to their CAME, an additional medical investigation is not conducted. Non-disclosure of medical symptoms/conditions to a CAME negates some of the safety benefit of examinations and increases the risk that pilots will be allowed to fly with a medical condition that poses a risk to safety.

In addition, although the family physician was aware that the pilot held a pilot's licence, there was a lack of awareness of the requirement to report to TC any medical conditions that may affect flight safety. This is consistent with the results of the TSB's discussions with other CAMEs and personal physicians. There may be a lack of awareness amongst Canadian general practitioners of the requirement to report medical conditions that may affect flight safety. This may result in a CAME not having all the information required to accurately determine a pilot's fitness for flight.

The guidelines contained in TP 13312 state that if the 10-year risk score, determined by using the risk scoring system (RSS), is 20% or greater, a cardiovascular assessment should be carried out. When using the RSS, an applicant's 10-year risk score can only be accurately determined if their cholesterol test results are known. However, a cholesterol test is not a required test under current standards; therefore, test results are only provided voluntarily, if known. Because CARs Standard 424 does not require an applicant to provide the results of a cholesterol test, there is a risk that CAMEs may not have all of the information needed to accurately determine an applicant's 10-year risk of a cardiovascular event.

Use of the RSS and the pilot's cholesterol results indicated a medium 16% risk score, which did not require further assessment. Had the pilot reported his elevated fasting blood sugar and serum triglyceride levels to the CAME, current Canadian medical protocol would have suggested a reassessment of the pilot's risk factor profile and additional tests in order to further ascertain his state of health. Additional tests, such as an exercise treadmill test, would likely have provided indications of the underlying heart disease. Despite multiple cardiac risk factors, the Canadian Aviation Medicine (CAM) system in aggregate (i.e. the pilot, the family physician, the CAME and the Regional Aviation Medical Officer [RAMO]) did not identify the pilot's underlying coronary disease.

In this case, neither the CAME nor the RAMO used the check boxes on the medical form or the RSS contained in the guidelines to consolidate and assess the applicant's risk level. Since TC's guidelines reference the RSS, it would be reasonable to expect that the TC medical examination report form would include a table consistent with what is published in the guidelines and that the guidelines would provide clear direction on its use. Because the CAMER form does not include the RSS table, there is a risk that cardiovascular risk factor information will not be recorded or used effectively when determining an applicant's risk of a cardiovascular event. The risk is exacerbated because the guidelines do not provide clear direction on the use of the table.

A full risk profile of this pilot would have included his age, obesity, BMI, smoking habits, hypertension, elevated triglycerides and blood sugar, as well as prompted further investigations to detect underlying coronary disease. These comprehensive investigations would likely have identified him as high risk for a cardiovascular event.

Findings as to causes and contributing factors

  1. The pilot's underlying coronary disease was not identified despite the defences built into the Civil Aviation Medicine system.
  2. The aircraft departed controlled flight and impacted terrain because the pilot suffered a heart attack.

Findings as to risk

  1. A lack of awareness amongst Canadian general practitioners of the requirement to report medical conditions that may affect flight safety may result in TC not having all the information required to accurately determine a pilot's fitness for flight.
  2. Non-disclosure of medical symptoms/conditions to a CAME negates the safety benefits of the examination and increases the risk that a pilot will fly with a medical condition that poses a risk to safety.
  3. TC guidelines for CAMEs do not adequately assess and document all cardiovascular risk factors in pilots, thereby increasing the probability that these risks will go undetected.
  4. When pilots do not wear their safety harnesses, they are at greater risk of injury during operation of the aircraft.

TSB Final Report A10H0004—Runway Overrun

Note: The TSB investigation into this occurrence resulted in a significant report, with extensive discussion and analysis on many issues such asaircraft tires, brakes, braking coefficient, precipitation, runway end safety area, runway maintenance, runway surface texture, runway surface condition, runway slope, grooving of runways, wet runway operations, hydroplaning and more. We have published the report’s summary, findings as to causes and contributing factors, and selected safety actions. Readers are invited to read the full report, hyperlinked in the title above. —Ed.

On June 16, 2010, an Embraer EMB-145LR, from Washington Dulles International Airport, landed at 14:30 EDT on Runway 07 at Ottawa/MacDonald-Cartier International Airport and overran the runway. The aircraft came to rest 550 ft off the end of Runway 07 and 220 ft to the left of the runway centreline. The nose and cockpit area were damaged when the nose wheel collapsed. There were 33 passengers and 3 crew members aboard. Two of the flight crew and one passenger sustained minor injuries. The TSB authorized the release of this report on April 17, 2013.

The EMB-145LR following the occurrence
The EMB-145LR following the occurrence

Findings as to causes and contributing factors

  1. The crew calculated an inaccurate VAPP (i.e., target approach speed) and flew the approach faster than recommended.
  2. The aircraft crossed the threshold 8 kt above VREF (i.e., threshold crossing speed), resulting in an extended flare to a touchdown of 2 270 ft, which was 770 ft beyond the operator’s desired touchdown point of 800 to 1 500 ft, but within the first third of the available landing distance as per the operator’s standard operating procedures (SOP).
  3. The smooth landing on a wet runway led to viscous hydroplaning, which resulted in poor braking action and reduced aircraft deceleration, contributing to the runway overrun.
  4. Rainwater accumulated on Runway 07/25 due to the crosswind and the design of its transverse slope, resulting in a further decline in the coefficient of friction for the occurrence flight.
  5. The crew did not select flaps 45, as encouraged by the operator’s SOP, for landing on a wet, ungrooved runway, which resulted in a higher landing speed and a longer landing distance.
  6. The crew did not initiate a go-around when VREF was exceeded by more than 5 kt indicated airspeed.
  7. The antiskid brake system operated as designed, by keeping the brake pressures from rising to commanded values after brake application in order to prevent the wheels from locking. With little braking action during the landing roll, the aircraft overran the runway.
  8. The aircraft overran the runway threshold and the runway strip and subsequently encountered a significant dip, where the nose landing gear folded rearward, resulting in substantial damage to the nose of the aircraft.

Steam cleaned marks observed on the departure end of Runway 07
Steam cleaned marks observed on the departure end of Runway 07

Safety action taken

Transportation Safety Board of Canada (TSB)

On March 2, 2011, the TSB sent an Aviation Safety Advisory to the Ottawa International Airport Authority, designating CYOW Runway 07/25 as "slippery when wet." This letter contained a review of the friction-testing requirements and the subsequent action required if the readings fall below prescribed limits. Also mentioned was the airport's requirement to provide a runway that is "so constructed as to provide good friction characteristics when the runway is wet." This requirement would include a proper profile of the runway to ensure "the most rapid drainage of water." A review of the profile of Runway 07/25 with respect to transverse slope revealed that this runway did not meet the minimum recommended practices of 1% specified in TP 312. The advisory concluded with a suggestion that the Ottawa International Airport Authority may wish to review its operational procedures, in conjunction with guidance contained in TP 312, and consider designating Runway 07/25 as being "slippery when wet."

Ottawa International Airport Authority

The Ottawa International Airport Authority conducted friction testing in April 2011. Although the testing showed friction values above the level at which corrective action would be required, some values along Runway 07/25 fell to a level at which maintenance action would be required. Pending rubber removal from Runway 07/25, planned for May 2011, the Ottawa International Airport Authority sent a NOTAM indicating that Runway 07/25 may be slippery when wet. This NOTAM was set to expire on June 15, 2011. The Ottawa International Airport Authority has been conducting friction testing on a monthly basis since April 2011. This testing included not only the TP 312 requirement for wetting the runway to a depth of 0.5 mm, but also completed tests using the international standard of 1 mm. Additionally, testing was completed during actual rainfall conditions. Based on the significantly higher friction levels achieved after rubber removal, the NOTAM was cancelled. Rubber removal was also conducted twice during this period. In October 2011, a Skidabrader was used to increase the friction levels of both Runway 07/25 and Runway 14/32.

In 2012, the Ottawa International Airport Authority resurfaced Runway 07/25 and corrected the runway camber and transverse slope. At the same time, taking into account the recommended practices of ICAO, it built a 300-m runway end safety area (RESA) at each end and was the first airport in Canada to do so.

Environment Canada

Environment Canada has published the Manual of Surface Weather Observations (MANOBS), 7th edition, Amendment 18, effective January 2013. MANOBS Section 10.3.5.6(c) has been amended to require reporting of changes in precipitation intensity criteria for issuing a SPECI (e.g., LGT [light] to MDT [moderate] or HVY [heavy]; MDT or HVY to LGT; MDT to HVY; or HVY to MDT).

Transport Canada

Transport Canada has published Advisory Circular No. 300-008: Runway Grooving, effective April 8, 2013. The purpose of the document is to provide information and guidance regarding the grooving of runway pavement.

TSB Final Report A10O0125—Stall and Spin and Collision with Terrain

On June 20, 2010, a Cessna 172K was returning to Toronto/Buttonville Municipal Airport after an aerial advertising and banner-towing flight. It flew a low approach parallel to Runway 33, dropped the banner in the grass and commenced an overshoot for landing on Runway 33. Shortly thereafter, the aircraft stalled and spun to the ground. The pilot was fatally injured and the aircraft was destroyed by the impact and a post-crash fire. The emergency locator transmitter functioned until it was consumed by fire. The accident occurred at 17:28 EDT. The TSB authorized the release of this report on April 13, 2011.

Analysis

Airport operations, ATC services and weather did not contribute to this accident. There was no indication of any difficulty in handling the aircraft with the banner in tow and it disengaged cleanly.

Records indicate that the aircraft was certified, equipped and maintained in accordance with existing regulations and approved procedures. There was no communication from the pilot indicating any difficulty. The pilot was certified and qualified for the flight in accordance with existing regulations. Fatigue was not considered a contributing factor.

In attempting to find a reasonable explanation as to why the aircraft stalled and spun to the ground, a number of plausible scenarios were considered:

  • the controls were fouled or jammed;
  • the aircraft was improperly configured;
  • the pilot became incapacitated or otherwise unable to control the aircraft;
  • the pilot's seat was not locked in position and slid on the rail;
  • the pilot attempted an emergency return to the runway; or
  • the pilot induced the pitch-up for some other reason.

The control cables were found intact and control surfaces were free to move. Aircraft manoeuvres throughout the low approach, banner drop and initial overshoot were all normal. Nothing was found to indicate that the controls were fouled or jammed in such a way to induce an abrupt pitch-up or prevent recovery.

The flaps were up and the pitch trim was found in the neutral position, a normal position for takeoff consistent with the banner drop sequence and subsequent climb at normal climb airspeed. In this configuration, in the absence of any pilot input, the aircraft could not autonomously achieve the pitch attitude or angle-of-attack that occurred in this accident.

If not properly secured, the seats of some aircraft, including Cessna types, have been known to slide backwards unintentionally on their rails. This may be due to acceleration forces on the initial takeoff or the pilot pushing on the controls to counter the trim change when power is applied on a go-around in the flap-down configuration. There is no known instance of seats sliding back in Cessna aircraft equipped with the 2007 secondary seat stop. Impact and fire damage made it impossible to determine with certainty whether or not the seat had been properly locked in position before impact or to determine its position at impact.

The investigation considered the possibility of an engine failure or other malfunction that would have led the pilot to attempt an immediate return to the field. It was determined that the propeller was turning at impact but not at full power. Examination of the engine, its components and ancillary controls did not reveal any anomalies that would have precluded normal operation. An engine failure from fuel starvation due to the non-standard selection of the right tank was considered unlikely.

On the go-around, the aircraft was to the left of the runway. Had the aircraft experienced an engine power loss, it is doubtful that the pilot would have turned to the left, away from the field; the more logical action would have been to turn right. Moreover, having been trained at Buttonville, in the event of an emergency landing, the pilot would likely have been aware of suitable landing sites in the vicinity of the departure area of Runway 33.

After dropping the banner, the pilot may have attempted to check the drop area by looking through the rear window. This would require pitching up deliberately and twisting the torso. With the left hand on the yoke and the right hand on the throttle, the twisting motion could have induced an inadvertent reduction in power and downward pressure on the left side of the yoke, resulting in a left bank. It is unclear how this would have resulted in a sustained power reduction and sustained application of aft elevator without the pilot taking notice and making corrections.

None of these scenarios could be validated.

Findings as to causes and contributing factors

  1. For undetermined reasons, during an intentional overshoot, the aircraft climbed, pitched up steeply, stalled and entered a spin from which it did not recover.
  2. The impact was not survivable.

TSB Final Report A10Q0132—Loss of Visual Reference with the Ground, Loss of Control, Collision with Terrain

Note: The TSB investigation into this occurrence resulted in a significant report, with extensive discussion and analysis on many issues such aspilot experience, weight and balance, weather, company management, regulatory oversight, spatial disorientation, pilot decision-making, pressures and more. Therefore we could only publish the summary, findings and safety action in the ASL. Readers are invited to read the full report, hyperlinked in the title above. —Ed.

On August 17, 2010, at 11:11 EDT, a Eurocopter AS350-BA helicopter departed from Sept-Îles, Que., under VFR for Poste Montagnais, Que., approximately 100 NM north of Sept-Îles. Fifty min after takeoff, the company's flight-following system indicated that the helicopter was 22 NM north of Sept-Îles and was not moving. A search was conducted and the wreckage was found on a plateau. There was no fire but the aircraft had been destroyed on impact. The pilot and the 3 passengers on board were fatally injured. No distress signal was received from the emergency locator transmitter (ELT). The TSB authorized the release of this report on January 23, 2013.

Photographs of accident site showing helicopter wreckage and breakup trajectory
Photographs of accident site showing helicopter wreckage and breakup trajectory

Findings as to causes and contributing factors

  1. For unknown reasons, the pilot did not take the fork in the Nipissis River but eventually had to turn back because of the clouds covering the terrain. This extension of the flight reduced the amount of fuel available to reach the destination.
  2. The pilot had reduced the fuel load to accommodate the large amount of baggage, thus decreasing flight endurance in the event of unforeseen circumstances. This decreased endurance is what probably prompted the pilot to take a shortcut towards the mountains in order to return to the original flight route.
  3. The pilot continued the flight in conditions that were below VFR weather minima specified in the Canadian Aviation Regulations (CARs), thus increasing the risk of losing visual reference with the ground.
  4. While the aircraft was flying in marginal weather conditions above the plateau, the pilot lost visual contact with the ground and then control of the aircraft, causing it to crash into the ground.

Findings as to risk

  1. When a large client charters a helicopter for a flight that cannot be carried out in compliance with the CARs, and the carrier agrees, the pilot is subject to tacit pressure to take off with an overloaded aircraft.
  2. When a large client’s passengers show up with excess baggage, they exert implicit pressure that could lead the carrier and pilot to allow an overloaded flight.
  3. When baggage is not weighed, the takeoff weight cannot be accurately calculated, and the helicopter may take off with weight in excess of the maximum allowable, thus increasing the risk of an accident due to overload.
  4. When inexperienced pilots face operational pressures alone without support from the company, they can be influenced to make decisions that place them and their passengers at risk.
  5. Transport Canada exercises little regulatory oversight of helicopter operations on the ground, and load details are not recorded in the logbooks. Consequently, there is no way of knowing whether a flight is overloaded on takeoff.
  6. Although the ELT emitted a signal, it was not picked up by the international satellite system for search and rescue (COSPAS-SARSAT) because the ELT’s antenna was severed. This may have delayed search and rescue efforts, affecting the survival of the occupants.
  7. Commercial helicopter pilots do not routinely practise instrument flying or regaining control of a helicopter with an unusual attitude solely with reference to the flight instruments. They are therefore at greater risk of losing aircraft control if they lose visual contact with the ground.

Other finding

  1. Programs for passenger awareness of flight conditions permitted by regulation may encourage passengers to question the pilot's decision to continue a VFR flight below the weather limits prescribed by regulation.

Safety action taken

Operator

The operator has taken the following remedial action since the accident on August 17, 2010.

  • The maintenance manager, avionics technician and a specialized firm are working on a Limited Supplemental Type Certificate (LSTC) to equip the entire fleet with digital flight instruments (Horizon and DG), which are more reliable than mechanical ones.
  • Additional management staff have been hired to increase pilot supervision.
  • A safety system manager position that does not report to the operations manager has been created.
  • Initial training of newly certified pilots is now much more extensive and involves 20 to 25 hr of dual instrument instruction.
  • Training on the ground and in flight has been introduced to reduce the risks of flying in bad weather.
  • An 8-hr decision-making and controlled flight into terrain (CFIT) avoidance course has been developed and is being delivered by an experienced pilot.
  • The operator is building an outdoor scale on the tarmac to check the real weight of goods loaded.
  • Every aircraft is now equipped with a portable hanging scale.
  • Personal scales are also available to pilots who ask for them.
  • Repeated requests have been made to the Société de protection des forêts contre le feu (SOPFEU) and to Hydro-Québec to install permanent scales at their bases of operations.
  • When accepting a charter request, the operator now tries to ascertain the client's real needs in order to recommend the appropriate helicopter.
  • Various weight and balance calculation tools are now available to pilots, e.g., an Excel spreadsheet and reimbursement for the purchase of iBal and Appventive (weight and balance apps).
  • Surprise audits are conducted to ensure pilots complete and respect the weight and balance forms and fly according to company standards.

Hydro-Québec

  • November 10, 2010: Hydro-Québec increased surveillance and validation of hours of flying experience as well as the training program for helicopter pilots used in Hydro-Québec charter flights.
  • November 25, 2010: at the annual meeting of the Association québécoise du transport aérien (AQTA), Hydro-Québec presented its employee awareness program, "La sécurité aérienne passe par le respect de certaines limites" [Air safety comes with compliance], and announced changes to its contractual requirements in order to secure the commitment of its helicopter providers to address concerns raised by incidents in 2010:
    • Flight in bad weather (VFR limit)
    • Takeoff with an overloaded aircraft (weight limit in the aircraft manual)
    • Flight within the height–velocity curve (altitude–speed)
    • Flight within less than 11 m of power lines and communication towers
  • January 2011: Hydro-Québec added an air safety component (respect of operational limits) to its helicopter provider evaluations.
  • April 2011: Hydro-Québec launched its employee awareness program. More than 20 sessions have been held so far for key user groups.
  • January 2012: Hydro-Québec added unannounced audits to its helicopter provider evaluations, particularly at job sites serviced by charters, to ensure, among other things, that loads do not exceed aircraft weight limits. Hydro-Québec now also requires its providers to implement a safety management system (SMS).
  • June 2012: Hydro-Québec launched its field surveillance program with surprise audits of charter flights and with a focus on specific issues of concern.
  • Certain clauses in contracts have been amended to ensure that weight and balance forms are completed for all flights conducted for Hydro-Québec. This aspect is checked during the unannounced audits.

TSB Final Report A11C0152—Freewheel-Assembly Malfunction During Practice Autorotation Landing

On September 13, 2011, a Bell 206B helicopter was on a local training flight at Thunder Bay International Airport, with a student pilot and instructor on board. The crew were using the threshold of Runway 30 as a designated landing area. At approximately 16:30 EDT, the student pilot entered a practice 180° autorotation to a planned power recovery. When the student initiated the power recovery, the rotor rpm decreased. The instructor took control and completed an autorotation. The low-rotor warning horn activated and remained on during the autorotation. The helicopter landed firmly yet not hard enough to activate the emergency locator transmitter. The rotor then struck the tail boom and the mast separated just below the rotor head. The helicopter was then shut down and the crew exited without injuries. There was no fire. The accident occurred during day visual meteorological conditions. The TSB authorized the release of this report on December 12, 2012.

Mast and pitch links
Mast and pitch links

Analysis

The crew responded decisively to an emergency, at a critical stage of flight in close proximity to the ground, and performed a successful autorotation landing. Neither environmental nor operational factors contributed to the occurrence. The analysis will address technical aspects relating to the helicopter's drivetrain.

Bell Helicopter Technical Bulletin 206-79-31 introduces a filter at the transmission oil outlet intended to prevent contamination of the restrictor. Although the filter was originally introduced to prevent particles of cut O-rings from contaminating the restrictor, it is likely that the filter would also be effective protection from other types of debris. This bulletin was optional and had not been incorporated, which increased the risk of restrictor contamination. The resulting reduction of oil flow may result in freewheel-assembly damage.

Since the installation of the freewheel assembly in March 2004, the aircraft had a relatively low annual utilization rate, averaging approximately 145 hr per year interspersed with periods of inactivity. Chapter 10 of the Bell Standard Practices Manual provides storage and reactivation procedures for aircraft preservation. However, there was no indication that these procedures were applied. The internal corrosion of the transmission oil cooler union, tube and freewheel assembly components predated the accident and indicated that water had been present in the transmission oil system. The transmission, oil cooler and piping had been installed in February 2002. Between then and March 2004, the aircraft flew approximately 722 hr, so it is likely that the corrosion developed later. The investigation could not determine the source of the water contamination. It is likely that condensation introduced moisture into the transmission and freewheel oil system during periods of inactivity. The presence of moisture in the oil system would have led to corrosion in the freewheel assembly and transmission oil cooler fittings. This was indicated by the iron oxide paste that coated the internal components of the freewheel, the pitting of the sprag surfaces, and the corrosion of the aluminum inlet union and magnesium outlet pipe attached to the transmission oil cooler. The pressure oil supply from the main rotor transmission to the freewheel assembly was reduced by a blockage at the restrictor (P/N 206-040-254-001) consisting of aluminum and magnesium corrosion products released from the transmission oil cooler union and pipe. The oil flow to the freewheel assembly was severely reduced. Operation without adequate lubrication resulted in damage and overheating of the already corroded internal components.

The freewheel assembly did not engage as the throttle was rolled on during a power recovery autorotation. As the helicopter was leveled with aft cyclic input, the rotor rpm began to decrease even though the engine began to spool up. The engine test runs indicated that an N1 rpm of 75% (12% above idle) was sufficient to accelerate an unloaded N2 gear train to approximately 104% N2 rpm. The rotor rpm decay indicates that the engine power was not being transmitted to the rotor system. When the sprag clutch suddenly engaged, the inertia built up in the N2 gear train was resisted by the mass of the decelerating main rotor, which resulted in the overstress failure of the mast. The acceleration of the lower portion of the mast instantly caused the pitch links to contact the swash plate drive link and break the collar set away from the mast. The swash plate outer ring was pulled around by the main rotor via the pitch links until the drive link rotated down and jammed against the inner (fixed) swash plate ring. The main rotor continued to decelerate and the pitch links wound around the spinning lower mast and pulled the main rotor blades to a nearly 90° negative pitch before failing in tension. As the main rotor came to a stop it flapped to one side and a blade bumped into the tail boom. The metal particles found in the transmission lower mast bearing support area were generated by the lower mast abrading against the upper mast stub. The lower mast came to a stop when the crew shut down the engine.

Findings as to causes and contributing factors

  1. At some point, moisture had entered the transmission oil causing contamination and corrosion of the internal components of the freewheel assembly and oil system.
  2. Blockage of the restrictor fitting in the oil supply line by corrosion products resulted in reduced oil flow.
  3. Operation of the freewheel assembly without adequate lubrication resulted in damage and overheating which impaired its proper functioning.
  4. When the damaged freewheel assembly did not engage, engine power was not transmitted to the rotor drive train during an attempted power recovery autorotation.
  5. After touchdown, the freewheel engaged and the resultant torque spike severed the main rotor mast and caused torsional damage to the entire drivetrain.

Findings as to risk

  1. If optional Bell Helicopter Technical Bulletin 206-79-31 is not incorporated, there is a risk that the restrictor may become contaminated. The resulting reduction of oil flow may result in freewheel assembly damage.
  2. If the procedures contained in Chapter 10 of the Bell Standard Practices Manual are not followed, there is a risk that corrosion may develop in aircraft components during periods of inactivity.

TSB Final Report A11W0144—Loss of Control and Collision with Building

On September 22, 2011, a float-equipped de Havilland DHC-6-300 Twin Otter was landing at the floatplane base (CEN9) located in Yellowknife, N.W.T., along the western shore of Great Slave Lake and beside the area known as Old Town. There were 2 crew members and 7 passengers on board; the first officer (FO) was the pilot flying. On touchdown, the aircraft bounced, porpoised and landed hard on the right float. The flight crew initiated a go-around; the aircraft lifted off at low speed in a nose-high, right-wing-low attitude and continued in a right turn towards the shore. As the turn continued, the aircraft's right wing contacted power lines and cables before the float bottoms impacted the side of an office building. The aircraft then dropped to the ground on its nose and cartwheeled into an adjacent parking lot. Both crew members were fatally injured, 4 passengers were seriously injured and 3 passengers sustained minor injuries. The aircraft was substantially damaged. The 406 megahertz emergency locator transmitter activated. There was no fire. The accident occurred at 13:18 MDT. The TSB authorized the release of this report on December 12, 2012.

Yellowknife floatplane base
Yellowknife floatplane base

Analysis

There was no indication that an aircraft system malfunction contributed to this occurrence. The analysis will focus on crew coordination and handling of the aircraft during the landing and attempted go-around.

When the crew briefed the approach, they were aware of the strong southerly winds and of the resulting rollers. To compensate for wind conditions, an approach speed above 80 kt was agreed upon, which is 10 kt above normal approach speed with full flaps. Airspeeds prior to touchdown were at or below 80 kt, as indicated by the captain’s two warnings. Strong westerly winds just prior to touchdown created crosswind and wind shear conditions over the intended landing area; these conditions were probably aggravated by the turbulence around The RockFootnote 1 immediately upwind of the touchdown zone. This combination would have resulted in airspeed fluctuations and caused the initial hard landing and bounce as the FO flared for the landing.

After the initial bounce, the aircraft would have been in a slow flight condition. The strong right crosswind and pilot aileron compensation likely caused the right float to contact the water before the left float during the second touchdown. The aircraft then yawed to the right, and the nose pitched down. Aft elevator control was used to counter the nose-down movement and to initiate the go-around. This, combined with the pitch-up effect of adding full power, resulted in the aircraft lifting off the water in a very nose-high, right-wing-low attitude. With full flaps selected and both wings in a stalled or semi-stalled condition, the aircraft could not accelerate or climb for the remainder of the flight. Since the captain assumed control without declaring that he had control, it is possible that both pilots were manipulating the controls during the go-around.

Causing or allowing the nose to continue to pitch up when full power was added during the go-around meant that the airspeed could not increase. This resulted in the wings stalling and a loss of control.

DHC-6 over docks during overshoot
DHC-6 over docks during overshoot

Findings as to causes and contributing factors

  1. Airspeed fluctuations at touchdown coupled with gusty wind conditions caused a bounced landing.
  2. Improper go-around techniques during the recovery from the bounced landing resulted in a loss of control.
  3. It is possible that confused crew coordination during the attempted go-around contributed to the loss of control.

Footnotes

Footnote 1

Southwest of the landing zone and the accident site in Old Town is a rock outcrop known as The Rock, rising about 70 ft above the lake and about 60 ft above the street. Located on top of The Rock is a public viewpoint, a private weather station, and the Pilot’s Monument. The aircraft was photographed from the public viewpoint throughout the approach, landing, overshoot and impact with the building.

Return to footnote 1 referrer

TSB Final Report A10W0155—Loss of Control and Collision with Terrain

On September 24, 2010, a privately operated Cirrus SR22 was on a round robin, VFR flight from Calgary/Springbank Airport (CYBW), Alta., to the area of Sundre, Alta., with three persons on board. About 5 NM northwest of Sundre, the aircraft entered a steep turning descent from about 1 600 feet AGL, striking the ground in a field at 13:47 MDT. The aircraft was destroyed by impact forces and a severe post-impact fire. No emergency locator transmitter (ELT) signal was received. The three occupants were fatally injured. The TSB authorized the release of this report on November 24, 2011.

History of flight

The aircraft departed CYBW at 13:19 for a planned 1.5 hr flight. The aircraft travelled northwest toward Sundre Airport (CFN7), 40 NM north of Springbank, at a maximum altitude of 6 500 ft ASL and a maximum ground speed of 160 kt.

The aircraft overflew CFN7 and conducted a right hand circuit, followed by a touch-and-go landing on Runway 32 at 13:41. After the touch-and-go, as the aircraft crossed the departure end of the runway, it oscillated slightly in the pitch axis.

The aircraft then climbed to approximately 5 600 ft  ASL, on a north-westerly heading, between 105 kt and 109 kt indicated airspeed (KIAS). At 13:43:50, the aircraft turned left to a heading varying between 220° and 227° magnetic (M). The aircraft maintained a relatively stable attitude with the bank angle varying between 5° left and right, and a pitch angle of approximately 5° nose up. At 13:44:21, the aircraft began to pitch to a maximum of 15° nose up, with no increase in either vertical speed or normal acceleration, and gradually descended to 5 500 ft ASL or 1 650 ft AGL. During this time, the airspeed gradually decreased from 130 KIAS to 67 KIAS.

At 13:45:35, the aircraft entered a right turn which increased in rate to a maximum of 11°/s. Airspeed increased to 98 KIAS, accompanied by an 80° nose-down pitch and a rapidly increasing rate of descent. Characteristics of this turn were consistent with the early stages of a spin. When the turn reached 329° M at 1100 ft AGL, the aircraft rolled to the left. At 13:45:48, the onboard recording quality was compromised due to extreme attitudes, resulting in loss of valid pitch and roll information.

At that time, the heading was decreasing to 120° M, airspeed was at 103 KIAS and the vertical descent rate was over 5 000 ft per min (fpm) with a positive loading in the vertical axis of 2.4 g. At 13:45:51, the last recorded data showed the aircraft 160 ft laterally from the impact point, with airspeed increasing through 132 KIAS, vertical descent rate increasing through 6 900 fpm and vertical acceleration reaching approximately 3.5 g. The engine was running throughout the descent to the ground.

Map of the last nine minutes of flight
Map of the last nine minutes of flight

Pilot and passenger history

The pilot-in-command, who occupied the left front seat, was issued a private pilot license in early 2005. He held a valid group 3 instrument rating, as well as multi-engine and night ratings. The pilot had accumulated about 567 hr total time, with 448 hr on the SR22. Prior to taking delivery of the SR22 in 2005, he was enrolled in an SR22 transition training program which normally consists of 7‑10 hr of ground instruction and 10‑15 hr of flight instruction. After 5.5 hr of ground instruction and 3.9 hr of flight instruction, weather conditions precluded completion of the training. He subsequently received at least 50 hr of dual instruction on his aircraft and later flew with the instructor for about 150 hr to improve his skills and remain current. The pilot was characterized as competent and cautious in his approach to flying.

The other two occupants were pilots who had purchased the occurrence aircraft on the morning of the accident. One occupant had held a private pilot license for fixed wing aircraft since 1985 and a glider pilot license since 1984. His total flight time in powered aircraft was about 165 hr, but with no hours in the SR22. The second occupant was a student pilot on fixed wing aircraft. He had completed most of the private pilot training program with 63 flying hr total flight time. His experience in the SR22 was limited to a 2 hr flight accompanying the owner from Springbank to Edmonton and back and a 1 hr familiarization flight with an instructor at Springbank. It was not determined which occupant sat in the right front seat on the accident flight.

Cockpit and flight controls of an SR22
Cockpit and flight controls of an SR22

Flight controls

The SR22 is equipped with dual controls, consisting of a single yoke handle protruding from the left and right sides of the instrument panel. Pitch control is accomplished by pushing and pulling the yoke in and out of the panel. For aileron roll control, the handle is rolled laterally from side to side. Spring forces in the system centralize the yoke in the neutral position in pitch and roll and compensate for increased feedback forces to the pilot as airspeed increases. The control principles are similar to most other light general aviation aircraft. However, some differences in the action and feedback forces usually require a short adjustment period for new pilots.

Analysis

The deceleration of the SR22, after the turn to the southwest, accompanied by a slight descent, is consistent with the engine operating at a reduced power setting and with the pilot attempting to maintain a more or less constant altitude. The slight loss of altitude and variation in heading suggests that the autopilot was disengaged.

The airspeed deteriorated to the point of aerodynamic stall, which was followed by entry to a spin to the right with a heading change of 90°. The aircraft behaviour in the continued descent indicates an over-recovery into a spiral dive in the opposite direction which featured rapid rotation, speed build-up and increasing positive vertical g loading. Insufficient altitude remained for recovery. The debris field and ground scars indicate that most of the rotation was stopped and a pull-up had begun immediately before the aircraft struck the ground at high speed in a nose down, slight left wing down attitude.

Aircraft handling by a passenger/pilot

With nearly 500 hr on the SR22, the pilot in the left seat, who is considered to be the pilot-in-command, would have been familiar with the handling characteristics and operation of the SR22. The passengers, who were also pilots, were relatively unfamiliar with the aircraft control and display systems and had little or no experience in flying from the right seat. Since the style and placement of the side-stick flight control and flight instruments were different from what either of the prospective owners were accustomed to, maintaining precise control of the aircraft from the right seat would have presented a challenge. Since the purpose of the flight was likely to familiarize the new owners with their aircraft, it is reasonable to assume that the right seat occupant was allowed to manipulate the flight controls. The behaviour of the aircraft during the departure from the touch-and-go at CFN7 was consistent with a pilot experiencing difficulty in maintaining precise control in the pitch axis. This would suggest that one of the purchasers, occupying the right seat, was in control at the time. The gradual deceleration while maintaining a constant altitude is consistent with engaging in slow flight. With the airspeed deteriorating to stall speed, mishandling of the controls could result in a wing dropping and a departure from controlled flight.

Non-deployment of the CAPS

Early recognition of situations justifying the activation and subsequent use of the Cirrus Airframe Parachute System (CAPS) has been very effective in reducing the severity of injuries and damage to aircraft. When the aircraft entered the initial spin at least 1 600 ft AGL, there was adequate height for a successful deployment as demonstrated by Cirrus research and past occurrences. In this occurrence, the condition of the T-handle retention bracket, combined with the location and condition of the deployed parachute in the wreckage, indicates that the system did not activate until ground impact. It could not be determined why the system was not activated.

Findings as to causes and contributing factors

  1. For undetermined reasons, the aircraft decelerated to the point of aerodynamic stall, followed by entry into a spin.
  2. The aircraft recovered from the initial spin entry and entered a spiral dive from which recovery was not accomplished before ground impact.
  3. For undetermined reasons, CAPS was not activated after the aircraft departed controlled flight.

Finding as to risk

  1. The listing of airworthiness directives (ADs) in the Transport Canada Continuing Airworthiness Web Information System for Canadian-registered SR22 aircraft contained incomplete service bulletin references and was incomplete in listing ADs applicable to the SR22. Although it was not the official source of ADs lists, there was a potential of misleading owners with regard to current maintenance requirements.

Other findings

  1. The occurrence aircraft was recently flown under IFR and in transponder airspace with incomplete maintenance actions.
  2. An AD which applied to flight controls was not complied with in the occurrence aircraft. Although this was not shown to have had a bearing on the accident, safety was not assured.
  3. It could not be determined who was flying the aircraft at the time of the loss of control.

Safety action taken

After this occurrence, Transport Canada revised the listing of ADs for the SR20/SR22 and referenced Cirrus Service Bulletins to accurately reflect the current information contained in the Continuing Airworthiness Web Information System.

TSB Final Report A11P0149—Loss of Control and Collision with Ground

On October 27, 2011, a Beechcraft King Air 100 departed Vancouver International Airport for Kelowna, B.C., with 7 passengers and 2 pilots on board. About 15 min after takeoff, the flight diverted back to Vancouver because of an oil leak. No emergency was declared. At 16:11 PDT, when the aircraft was about 300 ft AGL and about 0.5 SM from the runway, it suddenly banked left and pitched nose-down. The aircraft collided with the ground and caught fire before coming to rest on a roadway just outside of the airport fence. Passersby helped evacuate 6 passengers; fire and rescue personnel rescued the remaining passenger and the pilots. The aircraft was destroyed, and all of the passengers were seriously injured. Both pilots succumbed to their injuries in hospital. The aircraft’s emergency locator transmitter had been removed. The TSB authorized the release of this report on April 17, 2013.

Enlarged diagram of final flight path
Enlarged diagram of final flight path

Sequence of events

The aircraft had been in the hangar overnight, where it was inspected by the operator’s maintenance personnel. A litre of oil was added to the left engine, and all items of the inspection were signed off as complete.

The captain came into the hangar at about 14:20, spent approximately 2 min at the aircraft and then pulled the aircraft out of the hangar, where it was fuelled. The first officer (FO) joined the captain outside of the hangar while the aircraft was being fuelled. A complete preflight inspection of the aircraft was not conducted.

The aircraft’s engines were started, and the aircraft was taxied to pick up the passengers. During the loading of the passengers, a small puddle of oil under the left engine was pointed out to the pilots. The captain acknowledged the oil, but no further action was taken. The FO carried out the passenger briefing, which included a demonstration of the main door operation. The aircraft departed the fixed-based operator  (FBO) at about 15:35.

The aircraft departed CYVR at 15:41, on an IFR flight to Kelowna, B.C. The captain was the pilot flying. The flight was uneventful during its departure and climb to about 16 000 ft ASL. Approximately 15 min into the flight, the crew identified an oil problem. Oil was leaking from the left engine. The FO contacted ATC and received a clearance to return to CYVR. The captain initiated a turn toward CYVR and reduced the power for the descent. About 5 min after the turnaround, the abnormal checklist for low oil pressure was consulted.

The pilots decided that the approach would be flown normally, unless the oil pressure dropped below 40 lbs/sq. in., at which time they would follow the emergency checklist and single engine procedures. These procedures include a 10-kt addition to the VREF speed and feathering the propeller.

The crew received a visual approach clearance to Runway 26L via interception of the localizer. At about 7 NM from the runway and 1 500 ft ASL, ATC queried the crew about the need for emergency equipment. The crew declined the equipment and reported that everything was good for the moment. At 3.8 NM, with the runway in sight, the crew was cleared to land.

The flight was conducted without incident during the initial approach. Standard calls were made, which included the VREF speed of 99 kt. At 3 NM from the touchdown zone, the flaps were lowered to 30%. That was followed by the lowering of the landing gear to the down-and-locked position. From approximately 45 s before the upset, the crew’s activity increased. The flaps were lowered to 60%. The ground proximity warning system (GPWS) announced the AGL altitude in ft as “500.” The speed was announced as “105 kt,” then “VREF” (99 kt), and finally “VREF minus 5.” There was a change in the propeller noise and an immediate aircraft upset. The aircraft yawed left, rolled about 80° left and pitched nose-down about 50°. As the aircraft dove toward the ground, the wings returned to a level attitude and the nose came up, reducing the pitch to 30° nose-down. By that time, the aircraft had collided with the ground.

Asymmetrical thrust

On twin-engine aircraft where both engines turn clockwise, such as the Beechcraft King Air 100, the left engine is considered critical; this refers to the engine whose failure would most adversely affect the performance or handling qualities of an aircraft. When an engine becomes inoperative, a yaw effect will develop. The yaw effect varies with the lateral distance from the aircraft’s centreline to the thrust vector of the operating engine. This effect is amplified by the thrust produced by the operating engine. Due to the P-factorFootnote 2, the right engine develops its thrust vector further away from the aircraft’s centreline than does the left engine. The failure of the left engine will result in a larger yaw effect from the operating right engine.

Figure 6. Airplane Flying Handbook, FAA-H-8083-3A [US Government Printing Office, Washington DC: 2004], page 12−28. Modifications by TSB.)
Source: Airplane Flying Handbook, FAA-H-8083-3A [US Government Printing Office, Washington DC: 2004], page 12−28. Modifications by TSB.

Single-engine control

When thrust from engines off the centreline of an aircraft differs, control of yaw relies primarily on the tail’s vertical stabilizer and rudder and, to a lesser extent, the ailerons. The effectiveness of these surfaces increases with speed.

Most multi-engine, fixed-wing aircraft have a minimum control speed (VMC), which is the minimum speed at which the aircraft is directionally controllable with the critical engine inoperative. Below VMC, a pilot may not be able to control the aircraft. VMC for the accident aircraft was 85 kt, based on the inoperative engine propeller windmilling, a 5° bank toward the operating engine, takeoff power on the operating engine, retracted landing gear, flaps in the takeoff position and a most aft centre of gravity.

Information on the minimum speed at which directional control can be maintained with propellers not feathered and at normal rpm is not normally provided to flight crews. However, the propeller manufacturer calculated the drag produced by the aircraft’s 4-blade propeller, turning at about 1 900 rpm, to be about 300 lbs.

The application of asymmetrical thrust at low airspeed with both engines operating can result in a loss of directional control.

In August 2012, AvioConsult, an experimental flight test expert, published a review of the FAA Airplane Flying Handbook (FAA-H-8083-3A) with recommendations for improvement. The review specifically refers to “Chapter 12—Transition to Multiengine Airplanes” and recommends including more comprehensive information to ensure understanding of the aspects of asymmetrical thrust that can lead to a loss of control. Canadian publications also lack this valuable information.

Aerodynamic stall 

An aerodynamic stall occurs when the angle of attack of a wing exceeds the critical angle at which the airflow begins to separate. When a wing stalls, the airflow breaks away from the upper surface; the amount of lift will be reduced to below that needed to support the weight of the aircraft. While stalls occur at a particular angle of attack, they can happen at a variety of airspeeds. However, those airspeeds can be estimated for given conditions.

Information from ATC radar and the cockpit voice recorder (CVR) indicated that the aircraft was about 20 kt above stall speed, which was about 72 kt for the load factors present. Also, because the upset came with an apparent power increase, it was determined that a stall was not the initiating event.

Findings as to causes and contributing factors

  1. During routine aircraft maintenance, it is likely that the left engine oil reservoir cap was left unsecured.
  2. There was no complete pre-flight inspection of the aircraft, resulting in the unsecured engine oil reservoir cap not being detected, and the left engine venting significant oil during operation.
  3. A non-mandatory modification, designed to limit oil loss when the engine oil cap is left unsecured, had not been made to the engines.
  4. Oil that leaked from the left engine while the aircraft was repositioned was pointed out to the crew, who did not determine its source before the flight’s departure.
  5. On final approach, the aircraft slowed to below VREF speed. When power was applied, likely only to the right engine, the aircraft speed was below that required to maintain directional control; it yawed, rolled left and pitched down.
  6. A partially effective recovery was likely initiated by reducing the right engine’s power; however, there was insufficient altitude to complete the recovery, and the aircraft collided with the ground.
  7. Impact damage compromised the fuel system. Ignition sources, resulting from metal friction and possibly from the aircraft’s electrical system, started fires.
  8. The damaged electrical system remained powered by the battery; this resulted in arcing that may have ignited fires, including in the cockpit area.
  9. Impact-related injuries sustained by the pilots and most of the passengers limited their ability to extricate themselves from the aircraft.

Findings as to risk

  1. Multi-engine aircraft flight manuals and training programs do not include cautions and minimum control speeds for use of asymmetrical thrust in situations when an engine is at low power or the propeller is not feathered. There is a risk that pilots will not anticipate aircraft behaviour when using asymmetrical thrust near or below unpublished critical speeds and will lose control of the aircraft.
  2. The company’s standard operating procedures lacked clear directions for how the aircraft was to be configured for the last 500 ft, or what to do if an approach is still unstable when 500 ft is reached, specifically in an abnormal situation. There is a demonstrated risk of accidents occurring as a result of unstabilized approaches below 500 ft AGL.
  3. Without isolation of the aircraft batteries following aircraft damage, there is a risk that an energized battery may ignite fires by electrical arcing.
  4. Erroneous data used for weight-and-balance calculations can cause crews to inadvertently fly aircraft outside of the allowable centre-of-gravity envelope.

Footnotes

Footnote 2

P-factor is an aerodynamic phenomenon experienced by a moving propeller that is responsible for asymmetrical relocation of the propeller’s centre of thrust when an aircraft is at a high angle of attack.

Return to footnote 2 referrer

TSB Final Report A12C0053—Mid-Air Collision

On May 12, 2012, a privately registered Piper PA-28R-200 Arrow was approaching St. Brieux, Sask., on a flight from Nanton, Alta., with the pilot and 2 passengers on board. A privately registered Lake LA-4-200 Buccaneer amphibian was en route from Regina to La Ronge, Sask., with the pilot and 1 passenger on board. At approximately 08:41 CST, the two aircraft collided about 8 NM west of St. Brieux and fell to the ground at two main sites about 0.5 NM apart. Both aircraft, which were being operated in accordance with VFR, were destroyed and there were no survivors. There was no post-crash fire and the emergency locator transmitters did not activate. The TSB authorized the release of this report on June 11, 2013.

Wreckage of the Lake LA-4 200 in a marsh
Wreckage of the Lake LA-4 200 in a marsh

Analysis

There is no indication that either an aircraft malfunction or the weather contributed to this occurrence. In this occurrence, the two aircraft were following intersecting tracks. Consequently, there was a risk that they could arrive at the same point in space at the same time. The PA-28 began its descent near Saskatoon. In order to arrive at St Brieux’s elevation of 1 780 ft ASL, the pilot had to descend through 4 500 ft ASL (the LA-4’s altitude). Both aircraft arrived at the same point and altitude at the same time, which resulted in a mid-air collision. The rest of this section will explain how it is possible for two aircraft to collide while being operated under VFR.

The relative position of each of the occurrence aircraft just before the collision would have made visual acquisition difficult. The PA-28 was descending from a higher altitude than the LA-4. As a result, the PA-28 may have been obscured by the left wing of the LA-4. Likewise, the LA-4 may have been obscured from the PA-28’s pilot's view by the nose of the PA-28. The two diagrams indicate the positions of the aircraft relative to each other and the aircraft cockpit structures.

View from cockpit of the PA-28 indicating pilot's view partly obstructed by nose of aircraft
View from cockpit of the PA-28 indicating pilot's view partly obstructed by nose of aircraft (Note: Image not to scale.)

View from cockpit of the LA-4</i><i> indicating pilot's view partly obstructed by aircraft structure
View from cockpit of the LA-4 indicating pilot's view partly obstructed by aircraft structure (Note: Image not to scale.)

Both aircraft were transponder-equipped and had collision avoidance systems on board. The two aircraft were at or beyond the limits of the radar coverage required for these collision avoidance systems to operate. It is possible that one or both of the collision avoidance systems activated when the two aircraft were in range of each other and alerted either one or both of the pilots of an imminent collision. Depending on the detection range setting on the PA-28’s portable collision avoidance system (PCAS), the time available for evasive action could have ranged from 2 min to as little as 4 s.

Due to the limited experience of the LA-4’s pilot and the complexity of the presentation features of the traffic collision avoidance device (TCAD) system on board, it is unlikely that the pilot would have been proficient in its use and operating procedures even if the system had activated. Additionally, physiological issues related to vision may have further reduced the pilots’ available reaction time and resulted in their inability to avoid one another.

Relative positions of the aircraft at impact
Relative positions of the aircraft at impact

Inspection of the damage to both aircraft left wings and ailerons indicated that the pilot of the PA-28 might have banked to the left, turning northward and away from the LA-4. This type of evasive action would have resulted in the PA-28’s left wing being down to the point where it could only have come in contact with the left wing of the LA-4. A reconstruction of the likely aircraft positions at impact was prepared (see image above). The left outboard wing sections came to earth very close to each other and away from both main wreckage sites. 

This indicated that:

  • they were shorn off in the air at the time of the collision;
  • either one or both of the aircraft had initiated some sort of turning avoidance manoeuvre; and
  • because of the structural damage, both aircraft would have been uncontrollable after the collision.

The failure of the see-and-avoid principle to avert this collision illustrates the residual risk associated with reliance on that principle as the sole means of collision avoidance.

Both aircraft cabins were crushed upon impact with their respective water surfaces, indicating that the accident was not survivable for the occupants of either aircraft.

Findings as to causes and contributing factors

  1. Both aircraft arrived at the same point and altitude at the same time, which resulted in a mid-air collision.
  2. The converging position of the two aircraft relative to each other coupled with physiological vision limitations likely rendered visual detection extremely difficult. As a result, the available reaction time was reduced to a point where collision avoidance was not possible.
  3. The left ailerons and part of the wings from both aircraft were shorn off in mid-air during the collision. This would have rendered both aircraft uncontrollable and would have precluded either aircraft from recovering after the collision.

Finding as to risk

  1. Aircraft operating in VFR conditions are at continued risk of collision when the see-and-avoid principle is relied upon as the sole means of collision avoidance.

Other finding

  1. The design and operating features of the collision avoidance systems in the aircraft involved in this occurrence are such that they can inadvertently be set to detection parameters resulting in insufficient warning time for pilots.
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