Recently Released TSB Reports
- Issue 1/2013
- Copyright and Credits
- Guest Editorial
- To The Letter
- Flight Operations
- Maintenance and Certification
- Recently Released TSB Reports
- Accident Synopses
- The Civil Aviation Medical Examiner and You
- Take Five: Flying near Power Lines
- Know Where to Hold Short (poster)
- Full HTML Version
- PDF Version
- TSB Final Report A09W0105—Collision with Terrain
- TSB Final Report A09C0120—Loss of Control—Collision with Terrain
- TSB Final Report A09O0159—Tree Strike During Climb-Out
- TSB Final Report A09W0146—Loss of Control—Tail Strike
- TSB Final Report A09Q0131—Loss of Control and Collision with Cables
- TSB Final Report A10A0085—Collision with Water
- TSB Final Report A11P0027—Midair Collision
- TSB Final Report A11C0100—Collision with Terrain
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.
On June 15, 2009, a privately operated Beechcraft V35B Bonanza was on a VFR flight from Edmonton City Centre Airport, Alta., to view the Badlands area in the vicinity of Drumheller, Alta. When the pilot did not return by 1600, the family initiated the process to begin a search at 1700 on June 15, 2009. On June 16, Joint Rescue Coordination Centre resources from Winnipeg, Man., located the aircraft 12 NM northeast of Castor, Alta. The aircraft was destroyed by impact forces and the pilot, who was the sole occupant, was fatally injured. There was no post-impact fire.
No evidence was found to suggest that the aircraft's structure or systems malfunctioned.
The pilot was deemed to be fit and capable.
The vertical impact and the energy with which the aircraft struck the ground do not support a hypothesis of an aerodynamic stall.
Given the tendency for the aircraft to roll, the aircraft may have unintentionally entered into the initial stages of a spiral dive. If this were the case, the 90º impact angle of the aircraft would suggest that the spiral dive had progressed to vertical. The relatively low altitude at which the aircraft entered into this near-vertical attitude would have made recovery unlikely.
Without corroborating evidence to support any hypothesis, the cause of the accident could not be determined.
Finding as to causes and contributing factors
- For undetermined reasons, the aircraft departed controlled flight and crashed in an extreme nose-down attitude.
- The pilot had not filed a VFR flight plan detailing his intended flight path, which resulted in a delay in finding the aircraft by search-and-rescue resources.
On July 19, 2009, a privately operated Piper PA-46-310P Malibu departed Kamsack, on an IFR flight to Saskatoon, Sask. The pilot and three passengers were on board. At takeoff from Runway 34, the aircraft began rolling to the left. The aircraft initially climbed, then descended in a steep left bank and collided with terrain 200 ft to the left of the runway. A post-impact fire ignited immediately. Two passengers survived the impact with serious injuries and evacuated the burning wreckage. The pilot and third passenger were fatally injured. The aircraft was destroyed by impact forces and the post-impact fire. The accident occurred during evening civil twilight at 2124 CST.
The pilot was healthy and qualified. With 300 hr on the occurrence aircraft accumulated over 5 years, he would have been familiar with its operation and performance. The aircraft had no known defects and was operating within weight and balance limits. The runway was suitable for a normal takeoff, and weather conditions were benign. The pilot was known to be cautious and thorough; it is unlikely he deliberately operated the aircraft outside normal operating parameters.
The investigation could not identify a reason why the aircraft rolled to the left after takeoff. Consequently, a number of hypotheses were considered by the investigating team and are discussed in details in the analysis section of the final report at the link above. The list of hypotheses includes the following areas:
- Yaw effects
- Flap asymmetry
- Structural failure
- Automatic Flight Control System
- Left forward aileron drive cable
- Service letters and bulletins
Fractured left forward aileron drive cable assembly, as received at TSB Laboratory
Finding as to causes and contributing factors
- The pilot was unable to maintain aircraft control after takeoff for undetermined reasons and the aircraft rolled to the left and collided with terrain.
Finding as to risk
- The manufacturer issued a service bulletin to regularly inspect and lubricate the stainless steel cables. Due to the fact that the bulletin was not part of an airworthiness directive and was not considered mandatory, it was not carried out on an ongoing basis. It is likely that the recommended maintenance action has not been carried out on other affected aircraft at the 100-hr or annual frequency recommended in FAA SAIB CE-01-30.
Due to the complete destruction of the surrounding structure, restriction to aileron cable movement prior to impact could not be determined.
- The use of the available three-point restraint systems likely prevented the two survivors from being incapacitated, enabling them to evacuate the burning wreckage.
On June 3, 2009, a privately owned Cessna TU206G amphibious aircraft was taking off from Lake Muskoka near Torrance, Ont. On board were the pilot and one passenger. At approximately 1433 EDT, the aircraft became airborne, climbed initially to approximately 30 ft above the lake, and then continued climbing to approximately 90 ft above the lake. Shortly thereafter, the aircraft overflew a train trestle and began clipping trees on the shoreline. Several large trees were struck, resulting in substantial break-up of the aircraft. The aircraft struck the ground in an inverted attitude. A fire erupted after the ground impact and the majority of the aircraft was consumed by the fire. The two occupants were fatally injured. The emergency locator transmitter was destroyed and did not activate.
The investigation attempted to determine why the aircraft struck the trees after successfully becoming airborne and maintaining level flight. Photographic evidence did not reveal any abnormalities during the take-off run or initial climb, and propeller damage is consistent with considerable power being produced by the engine at the time of impact. Although the aircraft was substantially damaged by the impact and post-crash fire, the examination that was performed on the wreckage did not reveal any pre-impact failures.
The aircraft appeared to be properly configured for flight as per the recommended procedures in the Pilot Operating Handbook (POH). There was no evidence found related to a flight control problem that might have prevented the pilot from avoiding a collision with the trees. The aircraft was airborne approximately 5 500 ft before the shoreline, a distance that is within its performance capability to continue a climb that would have avoided the tree impact. The investigation revealed no evidence that either an internal or external distraction diverted the pilot's attention away from controlling the aircraft. It is possible that the pilot, with limited flight time in this aircraft during the past two years, misjudged the height of the trees along the shoreline. If the aircraft had developed a mechanical abnormality shortly after lift-off that would have affected its climb performance, the pilot would have had sufficient lake surface remaining to land the aircraft.
Estimated flight path
Findings as to causes and contributing factors
The aircraft struck the trees for undetermined reasons.
- A fire erupted after the ground impact, consuming most of the aircraft.
Transport Canada did not indicate a float endorsement on the current pilot's license although it had remained valid from the previous license issuance.
On August 4, 2009, a Robinson R44 Raven II helicopter departed Nahanni Butte, N.W.T., with a pilot and two passengers on board for a day VFR flight. At 1655 MDT, during an aborted landing on a narrow ridge in steep mountainous terrain, the helicopter turned 180º and descended down a slope. The tail boom struck the ground, and the helicopter tumbled down the mountainside, breaking up and coming to rest about 900 ft below the ridge. The helicopter was destroyed by a post-impact fire. The emergency locator transmitter on board did not transmit. The pilot survived with serious injuries, and both passengers sustained fatal injuries.
Note: canopy reflexions in bottom half of photo were not photoshopped to preserve integrity of photo. RCMP Photo.
There was no mechanical malfunction of the aircraft. Therefore, this analysis will focus on environmental, geographical and operating factors.
After overflying the ridge en route to the destination, the helicopter turned for a shallow approach, 60º to the ridge. The shallow approach was part of the recommended technique. The approach path downwind of the ridge, however, would have exposed the helicopter to subsiding air near the ridge. As the helicopter slowed through the speed where effective translational lift was lost before it entered the ground effect on the narrow ridge top, rotor pitch had to be increased substantially, accompanied by an increase in engine power. Since the helicopter’s ability to hover out of ground effect was marginal under ideal wind conditions, its ability to do so in subsiding air was substantially reduced.
With deteriorating rotor speed and aircraft controllability nearing the landing zone, the pilot was faced with three choices: overshooting straight ahead, landing hard on uneven terrain on the ridge top, or turning around and attempting to dive down the steep slope. The option of continuing straight ahead into wind posed a risk of injuring the ground party near the landing zone either by striking them on the overshoot or by subjecting them to injury from the helicopter had it rolled over on uneven terrain on the ridge top. Diving off the ridge may have afforded space to allow a reduction of main rotor pitch and a recovery of rotor speed. However, placing the helicopter downwind with deteriorating rotor speed precluded maintaining sufficient height above the ridge to avoid striking the tail on the ground.
The aircraft’s structural integrity was completely lost as it tumbled down the slope, with failure of the occupant retention systems.
Flight path and wind flow
Findings as to causes and contributing factors
The shallow approach downwind of the ridge placed the helicopter in an area of subsiding air, which increased the sink rate.
To overcome the sink rate, the pilot had to demand more engine power than was available, resulting in a loss of rotor speed.
To avoid injury to persons in the landing area, the pilot aborted the landing by turning 60º.
- During the aborted landing, the helicopter’s tail struck the top of the ridge, precipitating a fall down the steep shale slope, culminating in complete destruction of the helicopter and a post-crash fire.
On the morning of August 5, 2009, a private Enstrom F-28C helicopter took off from Mont-Laurier Airport, Que., on a local VFR flight over the town of Mont-Laurier to provide a television cameraman with a bird’s-eye of damage caused by a tornado. About 20 minutes later, as the helicopter was returning to the airport, the engine (Avco Lycoming HIO-360) experienced a power loss and backfiring. During an attempted emergency landing, the aircraft struck cables over Highway 117, struck the highway and rolled over in a ditch. The helicopter was completely destroyed in the post-impact fire. Both occupants were fatally injured.
Return path to Mont-Laurier Airport
Note: Due to space limitations, this analysis addresses mostly the actions of the pilot in handling the emergency. For additional information related to the partial power loss, to the maintenance of the aircraft, and to the pilot recency requirements, please see the full report at the link above.
The accident occurred following a partial loss of engine power at about 250 ft AGL over an area that provided no suitable site for a safe emergency landing. When the engine backfired, the pilot was probably surprised by the noise and the fishtailing caused by fluctuations in engine power.
The pilot had to continually make corrections by modulating the throttle to maintain constant rotor rpm as the engine power fluctuated. In addition, these changes in power also caused the torque effect induced by the main rotor to fluctuate, which then had to be counteracted with the tail rotor through pedal input to control the direction of flight.
The resulting difficulty in maintaining directional control due to the fluctuations in power increases a pilot's workload at a critical time when analyzing the situation, identifying the problem, choosing the correct procedure and taking appropriate action. After the partial loss of engine power, the pilot could not maintain rotor speed if he continued in level flight. The only option available that allowed him to maintain rotor speed was to descend.
Aircraft altitude at the time of the power loss is an important factor in the success of an autorotation and emergency landing. The greater the altitude above ground level, the more time the pilot has to find a suitable landing site. Flying at low altitude reduces that time to the point where it might be impossible to autorotate and set the helicopter down on a safe surface.
The power loss occurred when the helicopter was overflying a wooded area, and the choices for a suitable landing site were limited. If the engine ceases operating completely, the pilot has no choice and must make an emergency landing, irrespective of the condition of the surface below his flight path. However, if the engine is still producing power, it is possible to prolong the descent in order to find a suitable landing site.
At an altitude of 250 ft AGL, the pilot had about 15 seconds to execute an emergency landing. He had little time to select a suitable landing site. In addition, the pilot was faced with a dilemma: making an emergency landing on an unsuitable surface or continuing the flight until he found a suitable landing surface while rotor rpm continued to decay. The pilot continued the flight to find a section of the road that would be suitable for landing. Consequently, when the pilot finally arrested the descent about 20 ft above the road, the tail rotor effectiveness had diminished to a point where the helicopter was considerably yawed to the right of its horizontal track along the road.
To land with horizontal velocity, the aircraft must be aligned with the direction of travel, otherwise it could roll over. Consequently, the pilot had to correct to align the aircraft with the direction of horizontal travel before setting down on the road. The complex task of simultaneously arresting horizontal travel along the road with the helicopter yawed, controlling the descent until touchdown, and counteracting engine power fluctuations without a speed governor was particularly difficult.
When the loss of directional control to the right occurred, the already high workload associated with an emergency landing increased further, most probably creating work overload for the pilot. In a work overload situation, pilots often concentrate on a particular task and ignore the overall situation. As a result, the pilot probably focused his attention on the execution of the manoeuvre and did not see the cables spanning the road.
Emergency manoeuvres, particularly helicopter autorotation, are demanding and require a high degree of skill, precision and judgment. Moreover, a helicopter pilot often has less than one minute to execute an emergency landing after a complete engine failure. These skills can only be acquired with training and retained with practice.
Although the level of experience among pilots engaged in commercial operations is generally high, these pilots are required to make at least one recurrent training session in flight or on a simulator every year to practise these emergency procedures. Pilots engaged in private operations, however, are not subject to this flight training requirement as long as they conduct at least one flight every five years.
Findings as to causes and contributing factors
Fracture of the check ball retainer in the hydraulic tappet caused the malfunction of the No. 4 cylinder exhaust valve.
The malfunction of the No. 4 cylinder exhaust valve caused backfiring and partial loss of engine power. As a result, the aircraft could not maintain cruise altitude.
After the loss of engine power and during the following emergency landing, main rotor rpm decreased and caused a loss of directional control during the flare, followed by an impact with cables over the road.
- At an altitude of 250 ft AGL, the pilot had very little time to react to the loss of engine power, complete the autorotation manoeuvre and the emergency landing.
Findings as to risk
It is possible for a pilot to be in compliance with the Canadian Aviation Regulations' recency requirements without making a single flight with an instructor. Consequently, pilots in private operation could be inadequately prepared to deal with emergencies.
Owners of aircraft in private operation are not required to follow the recommendations of engine manufacturers. As a result, some aircraft parts can go without inspection or replacement for several years beyond the overhaul intervals prescribed by the engine manufacturer.
Some aircraft maintenance aspects were not in compliance with standards and requirements. Although these instances of non-compliance had no effect on the outcome of the occurrence flight, this practice could decrease the safety margin provided by the manufacturer.
- Not all airtime was recorded in the aircraft journey log, which increased the risk that the limits prescribed by the manufacturer would be exceeded.
The wear and erosion in the turbocharger was sufficient to prevent the engine from producing its full rated power under certain atmospheric conditions and, consequently, to limit the performance of the helicopter.
- The intensity of the post-crash fire prevented rescuers from extracting the occupants from the wreckage.
On August 5, 2010, a privately owned Cessna 414A departed Toronto/Buttonville Municipal Airport, Ont., en route to Sydney, N.S. The flight was operating under an IFR flight plan with the pilot-in-command (PIC) and the aircraft owner on board. Nearing Sydney, the aircraft was cleared to conduct an instrument approach. At the final approach waypoint the pilot was advised to discontinue the approach due to conflicting traffic. While manoeuvring for a second approach, the aircraft departed from controlled flight, entered a rapid descent and impacted the water at 2335 ADT. The aircraft wreckage was located using a side-scan sonar 11 days later, in 170 ft of water. The aircraft had been destroyed and both occupants were fatally injured. No signal was detected from the emergency locator transmitter (ELT).
The two occupants of the aircraft did not survive the accident. There were no witnesses to the final moments of the flight and there were no onboard recording devices to assist investigators. The aircraft impacted the water in a near vertical attitude, suggesting an in-flight loss of control. This analysis therefore focuses on possible scenarios explaining why the aircraft departed controlled flight and collided with the water.
Although the aircraft was extensively damaged by the impact, there was no evidence suggesting a problem with the flight controls or engines. All historic technical records were carried on the occurrence aircraft; only the most recent maintenance records could be reviewed as copies were retained by the facilities in Buttonville. This practice impeded the determination of the aircraft's maintenance history since new. The investigation ruled out turbulence as a factor for loss of control because there were no significant weather conditions in the area that could cause turbulence.
The PIC was communicating on the radio up until 1 min before the loss of control. During these communications, the PIC did not indicate any medical concerns or display any signs of impairment. This, coupled with the fact that the heater was recently overhauled and tested serviceable just days before the occurrence flight, allowed the investigation to rule out carbon monoxide poisoning. Pilot incapacitation was therefore not considered a contributing factor.
The PIC was in an unfamiliar aircraft, was flying in conditions which he did not like (night, inclement weather), and was operating into an unfamiliar airport. These factors would have contributed to the degradation of the PIC's conscious attention management capability. Simple tasks such as re-programming the GPS would have become difficult and may have taken attention away from flying for several minutes. Important steps were omitted such as reducing the airspeed or changing altitude when repeatedly instructed to do so. Additionally, the pilot turned to the left when instructed to turn right, and declined the offer for radar vectors which would have reduced pilot workload.
The owner had received limited experience flying a multi-engine aircraft 2 years earlier, had limited instrument flight experience and had not received any training on the occurrence aircraft or its systems. These factors would have contributed to the degradation of the owner's conscious attention management capability.
The aircraft track nearing OBVUP created a sharp closing angle on the OBVUP-GAGBU track. As the aircraft neared the OBVUP waypoint, the course track bar on the GPS would have moved very quickly toward the GAGBU waypoint. Due to the maximum rate of turn that an autopilot system allows, the aircraft would have flown through the OBVUP-GAGBU track before regaining course. To prevent this, a pilot would have to manually take control and initiate a steep turn. In an attempt to intercept the OBVUP-GAGBU course, an inexperienced pilot may try to follow the track bar using an increasingly steep bank angle. If this steep bank angle is left uncorrected, a spiral dive will result.
Aircraft flight path
The PIC and owner started their day in Calgary at 0800 (0500 local) and had been travelling for more than 15 hr. The training in Buttonville was carried out under conditions of high heat and humidity. During the final minutes of the flight, it is likely that the PIC and owner were task saturated. Although fatigue is not supported by any factual information received, the lengthy day may have exacerbated the level of task saturation. When a pilot is task saturated, the increased load on the conscious brain raises the potential for unrecognized spatial disorientation and/or loss of situational awareness. Erratic flying consisting of multiple heading and altitude excursions while the aircraft is flown manually is an indication that the pilot was possibly task saturated and disoriented. Spatial disorientation and the absence of a visible horizon have been identified as contributing factors to spiral dives. The radar track and the descent rate of the aircraft were indicative of a spiral dive. It is likely that the PIC and owner were both suffering some degree of spatial disorientation during the final portion of the flight. The crew was unable to recover control of the aircraft before contacting the surface of the water.
The investigation could not determine whether it was the PIC or the owner who was at the controls.
The PIC had arranged for a business meeting in Sydney on the morning of August 6, 2010. Self-imposed pressure to make this appointment likely influenced the crew's decision to depart Buttonville despite:
- their lack of experience on the aircraft type;
- their unfamiliarity with the destination airport;
- the night/IFR conditions; and
- the lengthy day.
Due to the severity of the impact damage, the aircraft likely sank quickly and the ELT would not have transmitted a signal. In 170 ft of water, attenuation would have masked the ELT signal if the ELT had withstood the initial impact.
Findings as to causes and contributing factors
It is likely that the PIC and the owner were both suffering some degree of spatial disorientation during the final portion of the flight. This resulted in a loss of control of the aircraft and the crew was unable to recover prior to contacting the surface of the water.
The PIC did not accept assistance in the form of radar vectors, which contributed to the workload during the approach.
- Self-imposed pressure likely influenced the crew's decision to depart Buttonville despite the flight conditions, lengthy day, and lack of experience with the aircraft and the destination airport.
It could not be conclusively determined who was flying the aircraft at the time of the occurrence.
The lack of onboard recording devices prevented the investigation from determining the reasons why the aircraft departed controlled flight.
- The practice of placing aircraft technical records on board aircraft may impede an investigation if the records are lost due to an accident.
On February 9, 2011, at about 1600 PST in daylight conditions, a group of four light aircraft took off from the Langley Regional Airport in Langley, B.C., for a local formation flight to Chilliwack, B.C. At about 1615, during a turn, the Cessna 150G and the Cessna 150L collided. The two aircraft briefly descended joined together and out of control, but at about 400 ft above ground level, they separated. The Cessna 150G broke up in flight and fell into a shallow slough; the two occupants were fatally injured and the aircraft was destroyed. The pilot of the Cessna 150L regained control of the aircraft and landed in a farm field without injury; however, the aircraft was substantially damaged as a result of the collision. There was no fire and the emergency locator transmitter (ELT) on the Cessna 150G activated upon impact with the slough.
History of the flight
Earlier that afternoon, a local group of four pilots and two crew members decided to carry out a short flight to practise formation flying in the Mission-Chilliwack area. The group comprised a Cessna 150G, a Cessna 150L, a Cessna 305A (L-19), and a Piper PA-28-180. The group assembled for a formation flight pre-flight briefing at the Langley Regional Airport, where all four aircraft were regularly based. As discussed at the meeting, the round-trip flight was a daylight recreation VFR flight to the Chilliwack Municipal Airport. Originally, the leader had planned to fly to, and land at, a popular site near Harrison Mills, B.C., and then conduct a debriefing on the ground. However, following a discussion about the remaining daylight, the leader chose to fly to Chilliwack instead. The pilots' intentions were to practise simple formation flying en route, during which they would carry out basic station-keeping (maintaining position) with simple turning manoeuvres, in a loose diamond pattern (Figure 1).
The briefing was straightforward and succinct, and did not include discussion of emergency or contingency procedures. However, a briefing was given by the leader about the join-up procedures, as well as instructions in the event a pilot could not find the formation, and about the formation break-out procedures at Chilliwack Municipal Airport.
Three of the pilots in the group were familiar with formation flying because they had flown together many times at various fly-past events and had practised over the Lower Mainland of B.C. As a newcomer to the group, the pilot of the Cessna 150L, having previously accompanied other pilots during two formation flights, was flying as the pilot of his own aircraft in the formation. The group planned to introduce the newcomer progressively to the basics of formation flying. They discussed having an observer/spotter fly with the pilot of the Piper PA-28-180 for the outbound leg to Chilliwack, and then change aircraft and return with the pilot of the C150L on the leg back to Langley. The pilot of the C150L, however, was unwilling to have another person in the aircraft with him because of likely distraction.
The lead aircraft was the Cessna 150G with two occupants on board. On the right-hand wing of the leader, in the number 2 position, was the Cessna 150L with only the pilot on board. Also in the group was the Piper PA-28-180, with two occupants on board, in the number 3 position on the leader's left side. The solo Cessna 305A (L-19) was in the number 4 position at the rear of the other three aircraft.
At about 1600, the four aircraft took off separately, but in a pre-arranged sequence, from the Langley Regional Airport and cleared the control zone to the north-east. In the next few minutes, the aircraft joined up and formed the diamond pattern as briefed. After the aircraft had settled in together, they flew in stable formation for several minutes as they proceeded eastwards in the Glen Valley, above the Fraser River, towards the township of Mission, B.C. During this time, the flight carried out gentle turns, with the flight leader communicating to the group on the appropriate radio frequency.
When the formation flight neared the township of Dewdney, B.C., at 1 500 ft ASL, about 1 450 ft AGL, and at a speed of 90 mph, the leader initiated a 15° angle-of-bank left turn for about a 90° heading change, and rolled out heading north. In preparation for this turn, the leader advised the number 2 aircraft (the C150L, on the outside of the turn) to increase engine power to account for the increased radius of turn. This instruction is in accordance with conventional station-keeping practice during formation flight, and was a practice this leader had often used with newcomers to the group. During this left-turn manoeuvring, the lateral distance and step-back of the number 2 aircraft on the leader's right side increased somewhat, but the C150L returned to its original position once the flight rolled out on the northerly heading (Figure 2).
Figure 2. Site map showing route of formation flight
Shortly after, the leader announced a right turn and this time advised the number 2 aircraft to reduce engine power since it was on the inside of the turn. The four aircraft then entered a level, 15° angle-of-bank right turn at 1 500 feet ASL to return to the southerly heading.
During the turn, the pilot of the number 2 aircraft (the C150L) lost sight of the lead aircraft (the C150G), turned away to the right and descended. After a brief interval, the C150L turned left and climbed while the pilot searched for the leader to rejoin the formation above.
At 1615, seconds after the leader called a roll-out, the two aircraft collided at almost 70° to each other (Figure 3). The aircraft began to rotate and descend joined together, and fell out of control for several seconds. At about 400 ft AGL, the aircraft separated; the C150G broke up in flight and fell into a shallow slough, while the pilot of the C150L regained control and landed the aircraft without engine power in a farm field.
Figure 3. Collision diagram
TSB laboratory flight path interpolation
The Transportation Safety Board of Canada (TSB) Laboratory examined the known flight path information and, using computer-assisted drawing and design software, estimated a plausible flight path for the two accident aircraft. Several assumptions were made as the basis for these calculations: 90 mph airspeed, 1 500 ft ASL altitude, and 15° angle-of-bank. It was assumed that the lead aircraft maintained the airspeed and the angle-of-bank throughout the manoeuvre, as there was no information to suggest otherwise. It was also assumed that the number 2 wingman aircraft (the Cessna 150L) did not slow down sufficiently to maintain the assigned formation station on the right wing of the leader.
Although it is possible that the aircraft in the formation flew at different speeds and angles of bank than the assumed values, the Laboratory calculations found that no significant variations occurred by using other values. For the purpose of understanding the basic dynamic situation of this accident, it is reasonable to use the assumed values in the analysis and recognize that there could be small inaccuracies.
In summary, the Laboratory analysis concluded that, during the entry to the right turn (Figure 4), the speed differential would have caused the C150L to overtake and lose sight of the leader. This would also have prevented the pilot of the C150L from seeing the leader during the last left turn before the collision. It was also concluded that the leader would have been unable to see the wingman aircraft approaching from the right side until it was too late to avoid contact.
Figure 4. Likely collision flight path (diagram not to scale)
Note: the comprehensive analysis section of the final report is too long to reproduce here and should be of interest to anyone involved or wishing to get involved in formation flight. For more please refer to the full report linked in the title of this summary.
Findings as to causes and contributing factors
During the right-hand turn in formation flight, the pilot of the C150L lost sight of the leader (the C150G).
After initially adopting a flight path that effectively eliminated the risk of collision, the pilot of the C150L turned back toward the leader so as to rejoin the formation, thereby unintentionally placing the aircraft on a course leading to their collision.
The high-wing configuration of the C150L significantly restricted the field of vision, and, during the left-hand turn, the pilot was unable to see the lead aircraft on a collision course.
The impact damage resulting from the in-flight collision rendered the C150G uncontrollable, and the aircraft was unable to maintain flight; it descended rapidly and collided with the terrain.
During its pre-flight briefing, the group had not discussed the contingency procedures for loss-of-sight of an aircraft, and it did not review the accepted practices for returning to the formation.
- For the occupants of the C150G, the forces of the in-flight impact and the collision with the terrain exceeded normal human tolerance, and the accident was not survivable.
Findings as to risk
Formation flying involving high-wing aircraft poses elevated risk due to the limited cockpit vision angles.
Formation flying involving aircraft of dissimilar aircraft types is challenging and demands higher skill levels, particularly when combining high-wing and low-wing aircraft. This aircraft combination creates an even greater risk for casual formation flyers.
Formation flying demands higher levels of skill, discipline, and training than conventional flying. Without appropriate formal training to achieve those increased levels, the risk of in-flight collision is elevated.
The ELT on board the C150G only transmitted on 121.5 megahertz (MHz), and the signal was only received by high-flying aircraft in the local area. When using such ELTs, there is a risk that the emergency situation will not be detected.
- Not having a qualified observer on board initial formation flights increases the risk of inappropriate pilot actions during loss-of-sight events.
Several civilian organizations in North America are dedicated to formation flying and collectively provide information, advice, and assistance for the pilot who wishes to participate in formation flying.
- Even though the two onboard GPS units were functioning at the time of the accident, no flight-path data for either aircraft were available to the investigation because neither GPS unit had been set up to record flight track. The absence of such data prevented the determination of the actual flight paths of the aircraft.
Safety action taken
Transport Canada (TC) issued a safety bulletin regarding the hazards surrounding formation flying. TC's Take Five “Formation Flight” brochure (TP 2228E-39) highlights the importance of pre-flight planning and flying skills in reducing the risks associated with formation flying. This Take Five was included in Issue 1/2012 of the Aviation Safety Letter.
From June 24 to 26, 2011, TC attended the annual Canadian Owners and Pilots Association (COPA) convention in Langley, B.C., and distributed the newest Take Five brochure dealing with formation flying. TC also presented information on a variety of related safety issues to the attendees.
On June 30, 2011, a float-equipped de Havilland DHC-2 departed from a lake adjacent to a remote fishing cabin near Buss Lakes, Sask., for a day VFR flight to Southend, Sask., about 37 NM southeast. There were four passengers and one pilot on board. The aircraft crashed along the shoreline of another lake located about 2 NM southeast of its point of departure. The impact was severe and the five occupants were killed on impact. The emergency locator transmitter (ELT) activated, and the aircraft was found partially submerged in shallow water with the right wing tip resting on the shore. There was no post-crash fire. The accident occurred during daylight hours at about 1111 Central Standard Time (CST).
Both the images recovered from the wreckage and the meteorological assessment indicate that the pilot had waited until the weather was suitable to accomplish the flight to and from Buss Lakes. The meteorological assessment suggested that light winds would prevail during the flights. Therefore, it is unlikely the flight encountered unusual winds or turbulence that would have led to the accident. The assessment suggested that local dense fog patches could have formed in the Buss Lakes area, possibly obscuring shorelines and/or higher terrain in the area. While it is unlikely the pilot would have flown into dense fog at low level, it is possible that manoeuvres had to be performed to avoid it. Fog patches near the aircraft would have been a distraction and would have contributed to the pilot’s workload.
Airframe and engine problems were not considered to be factors in the accident. The indications of a relatively high power setting at impact and the condition of the fuel pump suggest it is unlikely that the fuel pressure warning light was illuminated and a factor in the accident. Since the fuel pressure warning light illuminated at low power settings when taxiing, the minor stretching of the filament could have occurred on a previous flight.
Forward movement after impact was limited to 10 ft. While this can be attributed to the steep angle at impact, it also suggests low forward speed. Consequently, the speed was likely in the lower range of the airspeed marking of 50 to 83 mph. Likewise, the severe damage to the aircraft and limited forward movement suggests the rate of descent was likely at the higher end of the range of 500 to 1 200 ft/min identified on the instrument. A low forward speed, high rate of descent and steep angle are consistent with an aerodynamic stall. Consequently, while manoeuvring the aircraft, the pilot likely exceeded the critical angle of attack for the aircraft weight. Since the propeller appeared to be in a low pitch condition, suggesting that the propeller governor did not have time to adjust RPM, and the rate of descent had developed to only 1 200 ft/min, the stall likely occurred at low level, from an altitude that would preclude recovery. The weight of the aircraft and possible aft centre of gravity (CG) could have contributed to the aerodynamic stall.
The location of the accident site was close to, but not easily accessible from, the lake on which the fishing cabin was located. The aircraft’s heading to the southwest at impact rather than toward Southend, and its low altitude, suggest that the pilot was manoeuvring along the shoreline, possibly to permit the passengers to observe the area.
Findings as to causes and contributing factors
While manoeuvring at low level, the aircraft’s critical angle of attack was likely exceeded and the aircraft stalled.
- The stall occurred at an altitude from which recovery was not possible.
Findings as to risk
The separation of the propeller blade tip likely resulted from impact forces.
- The investigation could not determine whether the fuel pressure warning light was illuminated prior to the accident.
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