Recently Released TSB Reports

Recently Released TSB Reports


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 more information, contact the TSB or visit their Web site at www.tsb.gc.ca. —Ed.

TSB Final Report A07A0134—Touchdown Short of Runway

On November 11, 2007, a Bombardier Global 5000 departed Hamilton, Ont., for Fox Harbour, N.S., with two crew members and eight passengers on board. At approximately 14:34 Atlantic Standard Time (AST), the aircraft touched down 7 ft short of Runway 33 at the Fox Harbour aerodrome. The main landing gear was damaged when it struck the edge of the runway, and directional control was lost when the right main landing gear collapsed. The aircraft departed the right side of the runway and came to a stop 1 000 ft from the initial touchdown point. All occupants evacuated the aircraft. One crew member and one passenger suffered serious injuries; the other eight occupants suffered minor injuries. The aircraft sustained major structural damage.

Accident site.

Findings as to causes and contributing factors

  1. The crew planned a touchdown point within the first 500 ft of the runway to maximize the available roll-out. This required crossing the threshold at a height lower than the manufacturer’s recommended threshold crossing height (TCH).

  2. The flight crew members flew the approach profile as they had done in the past on the smaller Bombardier Challenger 604 (CL604), with no consideration for the Global 5000’s greater aircraft eye-to-wheel height (EWH), resulting in a reduced TCH.

  3. The abbreviated precision approach path indicator (APAPI) guidance, although not appropriate for this aircraft type, would have assured a reduced main landing gear clearance of 8 ft above threshold. At 0.5 NM, the pilot flying (PF) descended below the APAPI guidance, further reducing the TCH.

  4. The pilot used the wing-low crosswind technique, increasing his workload and resulting in pilot-induced oscillations.

  5. Both pilots’ low experience on the Global 5000, combined with the PF’s high workload, affected their ability to recognize the unsafe approach path and take appropriate corrective action.

  6. With the aircraft in a low energy state, the pitch up to 10.6° without an associated thrust increase could not correct the flight profile, resulting in the impact with the sloped surface before the runway threshold.

  7. The impact with the sloped surface initiated a sequence resulting in the collapse of the right main gear, a loss of directional control, the eventual departure from the runway surface, substantial damage to the aircraft, and some injuries.

  8. Contrary to the manufacturer’s recommended practices, the operator’s standard operating procedures (SOPs) sanctioned descent under electronic or visual glide slope guidance, with a view to extending the landing distance available as acceptable and good airmanship; this contributed to the aircraft landing short of the runway.

  9. The lack of an effective transition from traditional safety management to a functional safety management system (SMS) as required by the operator’s private operator certificate (POC) prevented an adequate risk assessment of the introduction of the Global 5000 into its operations and contributed to the accident.

  10. An inappropriate balance of responsibilities for oversight between the regulator, its delegated agency, and the operator resulted in the operator’s inadequate risk assessment not being identified.

Aircraft in relation to vertical path (VPTH) and APAPI path
Aircraft in relation to vertical path (VPTH) and APAPI path

Aircraft attitude at threshold
Aircraft attitude at threshold

Findings as to risk

  1. Because aircraft EWH information is not readily available to pilots, crews may continue to conduct approaches with an aircraft mismatched to the visual glide slope indicator (VGSI) system, increasing the risk of a reduced TCH safety margin.

  2. Due to limited knowledge of the various VGSI systems in operation and their limitations, flight crews will continue to follow visual guidance that might not provide for safe TCH.

  3. The operator did not develop an accurate company risk profile. This precluded identification of systemic safety deficiencies and development of appropriate mitigation strategies.

  4. If adequate safety oversight of POC operators is not maintained by the regulator, or the delegated organization, especially during SMS implementation, there is an increased risk that safety deficiencies will not be identified.

  5. The fact that the Canadian Business Aviation Association (CBAA) did not insist that milestones for SMS implementation and development be followed may result in some POC operators never reaching full SMS compliance.

  6. If Transport Canada does not ensure that the CBAA fulfills its responsibilities for adequate oversight of the Canadian Aviation Regulations (CARs) subpart 604 community, safety deficiencies will not be identified and addressed.

  7. The audit of the operator’s SMS, conducted by the CBAA-accredited auditor, did not identify the deficiencies in the program or make any suggestions for improvement. Without a comprehensive audit of an operator’s SMS, deficiencies could exist resulting in the operator’s inability to implement an effective mitigation strategy.

  8. Contrary to the recommendations made in the Transport Canada/CBAA feasibility studies, the CBAA did not have a quality assurance program for its audit process. As a result, there is a risk that the CBAA will fail to identify weaknesses in the POC audit program.

  9. At the time of the accident, no one at Fox Harbour (CFH4) had been assigned responsibility for regular maintenance of the APAPI, therefore preventing timely identification of APAPI equipment misalignment.

  10. The operator’s risk analysis before the introduction of the Global 5000 did not identify the incompatibility between the EWH of the aircraft and the APAPI at CFH4.

  11. Not wearing shoulder harnesses during landings and takeoffs increases the potential risk of passenger injuries.

  12. Passengers not wearing footwear could impede evacuation, increase the risk of injury, and reduce post-crash mobility and (potentially) survival.

Note: Due to space consideration we could only reproduce the summary and the main findings. Readers are strongly encouraged to read the complete TSB Final Report A07A0134 on the TSB’s Web site at www.tsb.gc.ca. This comprehensive and significant report explains in detail all of the issues identified in the findings. —Ed.



TSB Final Report A07O0305—Runway Incursion

On November 15, 2007, a Learjet 35A was taxiing from the north end general aviation ramp for departure on Runway 06L at Toronto/Lester B. Pearson International Airport (LBPIA), Ont., bound for Chicago/Rockford, Ill. The crew of the Learjet was instructed to taxi on Taxiway Juliett, hold short of Taxiway Papa, and subsequently taxi on Taxiway Foxtrot and hold short of Runway 05. At 22:06:34 Eastern Standard Time (EST), the airplane arrived at the hold position for Runway 05, failed to stop, and, at 22:06:43 EST, it entered the runway. At that time, an Israel Aircraft Industries IAI 1124 Westwind airplane was on the landing roll on Runway 05. The crew of the Westwind observed the Learjet in front of them and manoeuvred to pass behind it. The two aircraft came within 60 ft of each other.

Factual information
Departing Toronto/LBPIA, the Learjet’s co-pilot obtained a clearance to “taxi right on Juliett and hold short of Papa.” The crew understood the clearance, correctly read it back, and made no request or gave any indication that they required progressive taxi instructions. Before reaching Taxiway Papa, air traffic control (ATC) instructed the crew to “taxi onto Foxtrot and hold short of Runway 05.” The co-pilot read back the instruction correctly and proceeded to carry out the taxi-before-takeoff checklist. The pilot-in-command (PIC) had an aerodrome chart. He taxied the airplane while looking for the Runway 05 holding point and responding to the co-pilot on checklist items. The PIC saw lights in the distance that he believed to be Runway 05 and crossed what appeared to him to be a taxiway but was, in fact, Runway 05.

Neither pilot was aware that the aircraft was entering Runway 05 and neither saw the Westwind on the runway until after being advised by ATC. The co-pilot’s head was down performing the checklist.

The Westwind had been cleared to land on Runway 05. The crew saw the Learjet after it entered the runway and was illuminated by the Westwind’s landing lights. The Westwind crew avoided the Learjet by using brakes and steering left to pass behind. It was a clear night with unrestricted visibility. There were no visual obstructions between the two aircraft during the Westwind’s approach and landing. At the time of the incident the Toronto/LBPIA control tower was staffed by 10 controllers—7 active and 3 available. Their workload was considered light to moderate. The North Tower, South Tower, North Ground, and South Ground were all staffed.

The North Tower controller was controlling the Westwind on its approach. The runway was clear when the landing clearance was given and was still clear when the Westwind crossed the threshold.

In addition to the Learjet, the North Ground controller was controlling four other aircraft—three taxiing and one under tow—which were on the east side of Runway 15L/33R, in a different direction from the Learjet, as shown in Figure 1. The North Ground controller communicated with three of these aircraft in the 60 s prior to the incursion and was monitoring the fourth as it was reaching its clearance limit. Within 10 s of the incursion, with the Westwind on the landing roll, the North Ground controller scanned back to the Learjet, which was approximately 1 mi. away, travelling directly toward the control tower.

 Figure 1: Aircraft positions
Figure 1: Aircraft positions

Click on image to enlarge.

It initially appeared to the North Ground controller that the Learjet would stop short of Runway 05 as instructed. The North Tower controller expressed doubt and the North Ground controller checked the airport surface detection equipment (ASDE) display and determined that the Learjet was entering the runway. At about the same time, an aural conflict alarm sounded.

Analysis
This incident occurred when the Learjet’s pilot misidentified Runway 05 as being in the distance and continued to taxi into the path of a landing airplane despite the following passive measures intended to defend against crew deviations:

  • airfield markings and signage complied with relevant standards;

  • signs and markings were unobstructed and visibility was good; and

  • ATC instructions complied with relevant standards, were clearly understood, and were read back correctly.

The crew did not correctly perceive their location on the airfield. None of the indicators of the hold-short point were prominent enough to attract their attention and overcome their perception that they were proceeding correctly. Potential factors contributing to their reduced level of awareness are familiar from previous studies:

  • the incursion occurred while taxiing out;

  • only one crew member was monitoring the taxi route and compliance with the instruction;

  • distraction by the before-takeoff checklists;

  • night lighting conditions;

  • fatigue associated with the third leg of the day at the 12-hr point of the crew duty day; and

  • operational pressure (self-imposed because the crew would be at the limit of their crew day by the time they reached home base).

Findings as to causes and contributing factors

  1. Both crew members of the Learjet were unfamiliar with Toronto/LBPIA and did not correctly perceive their position on the airfield. As a result, they did not hold short of the runway as instructed by ATC and unintentionally proceeded onto the runway into the path of a landing airplane.

  2. The co-pilot did not assist in monitoring the taxi route or compliance with instructions because he was carrying out checks while the PIC taxied the aircraft.

Findings as to risk

  1. A crew’s alertness may have been reduced by operational pressures and fatigue associated with a long duty day and multi-leg scheduling.

  2. The runway incursion monitoring and conflict alert system (RIMCAS) does not provide sufficient time to prevent incursions, nor does it provide sufficient warning to allow air traffic controllers to avert a collision.

  3. There is currently no automated runway incursion warning system to warn flight crews directly of impending incursions or conflicts.



TSB Final Report A07C0225—Double Engine Power Loss

On November 30, 2007, an Aero Commander 500B departed from Dryden, Ont., en route to Geraldton, Ont. The flight was conducted under VFR at 5 500 ft above sea level (ASL) with ambient temperatures aloft of -33°C. Approximately 40 min into the flight, the crew observed an abnormal right engine fuel flow indication. While troubleshooting the right engine, the engine RPM and fuel flow began to decrease and the crew diverted toward Armstrong, Ont. A short time later, the left engine RPM and fuel flow began to decrease and the crew could no longer maintain level flight. At 09:17 Central Standard Time (CST), the crew made a forced landing 20 NM southwest of Armstrong, into a marshy wooded area. The captain sustained serious injuries and the co-pilot and passenger sustained minor injuries. The aircraft was substantially damaged. The crew and passenger were stabilized and transported to Thunder Bay, Ont., for medical assistance.

Start by simply indicating what you believe is malfunctioning. Then, indicate how it is malfunctioning.

During examination of the aircraft at the accident site, a restriction or blockage was found in the fuel supply to both Lycoming I0-540-B1A5 engines. The left engine had a partial blockage with no fuel supply to the forward cylinder nozzles; the right engine had a complete blockage with no fuel supply to any of the cylinder nozzles. The blockage was determined to be within the fuel distributor valve(s) because fuel pressure was present upstream of the valves (see Photo 1). The location of the fuel distributor valve on the Lycoming IO-540-B1A5 engine, in conjunction with the Aero Commander 500B engine cowling configuration, exposes the valve directly to the cooling blast of the outside air.

The right engine fuel distributor valve was removed and examined. Ice was found adhering to the internal main metering well surface (see Photo 2). Ice formed from super-cooled water droplets was also found adhering to the servo bleed screen and fully covering and blocking the return-to-tank bleed orifice (see Photos 3 and 4).

Photo 1: Fuel distributor valve installation in thelower front engine area
Photo 1: Fuel distributor valve installation in the
lower front engine area

Photo 2: Ice on main metering well
Photo 2: Ice on main metering well

Photo 3: Super-cooled droplet ice formationon the servo bleed screen
Photo 3: Super-cooled droplet ice formation
on the servo bleed screen

Photo 4: Return-to-tank bleed orifice(shown frozen and thawed for comparison)
Photo 4: Return-to-tank bleed orifice
(shown frozen and thawed for comparison)

Findings as to causes and contributing factors

  1. Suspended water in the fuel system precipitated out of solution and froze in the fuel distributor valve. This blocked the fuel supply to the fuel nozzles and led to the loss of engine power.

  2. The aircraft was being operated without a fuel additive icing inhibiter. Use of such an additive would have inhibited ice formation in the aircraft’s fuel system and would likely have prevented the fuel system blockage.

Findings as to risk

  1. The fuel distributor valve on the Aero Commander 500B is exposed directly to the cooling blast of the outside air, which, under extremely cold conditions, can lead to the freezing of super-cooled water droplets present in the fuel stream.

  2. The operator did not have procedures to describe how fuel additive icing inhibiters should be used during winter operations.

Safety action taken
The operator mandated the use of fuel additive icing inhibitors in conditions where the ambient temperature, either at the surface or at altitude, is less than 0°C. The use of fuel additive icing inhibitors has been incorporated into the company operations manual, sub-section 4.2.2—Fuel Anti-icing Additives. The company planned to introduce mandatory training on the use of fuel additive icing inhibitors in the fall of 2008.



TSB Final Report A08Q0055—Landing with Nose Wheel Retracted

On March 20, 2008, a Challenger CL-600-2A12 was conducting an IFR flight from the Bonaventure Airport, Que., to the Québec/Jean Lesage International Airport, Que. During the approach, the nose gear failed to extend. The flight crew did a low fly-pass, and the tower controller and an aircraft maintenance engineer (AME) confirmed the nose gear anomaly. The flight crew went through the checklist and prepared the six passengers for a landing with the nose gear retracted. At 06:43 Eastern Daylight Time (EDT), the aircraft landed on its nose. Damage was limited to the nose-landing-gear doors and the nose-landing-gear well structure. There were no injuries.

Challenger CL-600-2A12

Findings as to causes and contributing factors

  1. The oleo pneumatic shock absorber (oleo strut) was found to be compressed due to a loss of nitrogen. As a result, the nose landing gear was released from the landing gear uplock latch, which allowed the wheel assembly to pivot and become jammed in the well.

  2. The right deflector remained jammed in the nose landing gear well, preventing extension of the landing gear.

Findings as to risk

  1. The design of the landing gear latch and pin allows the landing gear to be released from the landing gear uplock latch and to drop into the well during flight, causing the right gravel deflectors to jam, and preventing extension of the nose landing gear.

  2. The clearance between the gravel deflectors and the nose landing gear well structure is very narrow when compared to similar aircraft that are not equipped with gravel deflectors. Another oleo pneumatic shock absorber (oleo strut) compression could result in the same situation occurring again.



TSB Final Report A08C0171—Engine Power Loss and Forced Landing

On August 8, 2008, a Cessna 207A was departing from Winnipeg/St. Andrews Airport, Man., en route to Bloodvein River, Man., with one pilot and three passengers on board. Shortly after takeoff, the aircraft’s engine performance deteriorated and several engine backfires were noted. The pilot attempted to return to Winnipeg/St. Andrews Airport but the aircraft could not maintain altitude. The pilot carried out a forced landing on Provincial Highway 8, approximately 2 NM north of the airport at 13:56 Central Daylight Time (CDT). The aircraft was not damaged and none of the aircraft occupants was injured.

The engine magneto timing was checked and both magnetos were found to be incorrectly timed. The required timing is 22° before top dead centre (BTDC) on the compression stroke on the No. 1 cylinder piston. The magnetos were found to be timed to approximately 50 to 60° BTDC. Such an advanced timing of the magnetos leads to pre-ignition or detonation of the combustion gases in the engine and results in high cylinder head temperatures and engine power loss.

A 50-hr inspection of the aircraft was started on July 28, 2008, and completed on the day of the occurrence. In conjunction with this inspection, a 500-hr inspection of the Slick 6310 magnetos was carried out in accordance with Slick Service Bulletins SB2-08 and SB3-08. Though there is no colour vision requirement to hold an aircraft maintenance engineer (AME) licence, the engineer who removed and installed the magnetos had a red/green colour vision deficiency and was incapable of discerning reds or greens.

The Cessna 207 series service manual indicates that the advanced firing position of the No. 1 cylinder may be determined by the use of a timing disc and pointer, Time-Rite piston position indicator, protractor and piston locating gauge, or external engine timing mark reference. The external engine timing marks are located on a bracket attached to the starter adapter, with a timing mark on the alternator drive pulley as the reference point. These marks consist of indented lines on the parts in question.

The engineer chose the external engine timing mark reference as the method of timing because the external magneto timing indicator plate was present on the engine. The external magneto timing indicator plate is located on the rear of the engine, in a dimly lit area of the engine bay. The mark on the alternator drive pulley had been painted red for conspicuity during the last engine overhaul.

The engineer brought the engine around to the compression stroke on the No. 1 cylinder piston and aligned the mark on the alternator drive pulley with the 22° BTDC position on the external engine timing plate. The engineer removed the magnetos and sent them to the engine overhaul facility for the 500-hr inspection compliance.

During the eight-day period in which the magnetos were away for inspection, the engineer completed other maintenance tasks on the aircraft as required by the 50-hr inspection chart. The engine bay was dirty and the engine and belly of the aircraft were washed with solvent. Upon return of the magnetos, the engineer reset the engine timing to the 22° position because the propeller had been turned during the servicing of the aircraft.

As the engineer rotated the propeller to align the timing marks, the first mark that came into view on the alternator drive pulley was a scratch that had snagged debris from the engine washing (see Photo 1). The scratch, with the embedded debris, looked similar in appearance to the correct timing mark (see Photo 2). The engineer was not able to discern the red paint colouring to cross-reference the mark and chose the scratch as the timing mark of reference. The correct timing mark was out of view on the opposite side of the pulley. The engineer installed the magnetos using the scratch with the embedded debris as the reference point.

Photo 1: Mistaken timing mark with debris removed
Photo 1: Mistaken timing mark with debris removed

Photo 2: Correct timing mark
Photo 2: Correct timing mark

Finding as to causes and contributing factors

  1. During recent maintenance work, both engine magnetos were incorrectly timed. This condition was not detected during the subsequent engine ground run or before the flight. The incorrect magneto timing led to pre-ignition or detonation of the combustion gases in the engine, which resulted in high cylinder head temperatures and engine power loss after takeoff.

Finding as to risk

  1. Service Bulletin M84-8 and Mandatory Service Bulletin (MSB) 94-8C regarding preferred magneto timing methods were evaluated by the operator and not incorporated into its approved Cessna 207 maintenance schedule. The continued use of the external engine timing mark method increased the risk of a magneto timing error.

Other finding

  1. A maintenance evaluation sheet addressing the evaluation of MSB 94-8C was not prepared by the company in accordance with its maintenance control manual (MCM).

Safety action taken
Cessna indicated that it will be incorporating information in MSB 94-8C into the next scheduled revision of the Cessna 207 maintenance manual.

The operator indicated that it will be making changes to its policy regarding the implementation of service bulletins.



TSB Final Report A08P0265—Loss of Control— Collision with Terrain

On August 13, 2008, a Bell 206L (LongRanger) helicopter was being operated at Legate Creek, just north of Terrace, B.C. At about 10:30 Pacific Daylight Time (PDT), the pilot started longline operations to move a drill rig at about 4 200 ft above sea level (ASL) on a steep hillside. The first and second lifts were completed uneventfully. Upon lifting the third load, the helicopter descended into the valley before it climbed slowly. It needed two orbits to climb to a sufficient height to make its approach to the landing area. When the load was about 3 ft above the drill deck, the helicopter descended rapidly and the load came down hard. While the ground crew attempted to unhook the load, it popped back into the air. The load slammed onto the deck again and the helicopter fishtailed. The load was abruptly lifted back into the air once again and the helicopter began to spin with its tail bent. The load remained attached to the helicopter and became lodged in trees. Tethered by the longline, the spinning helicopter descended in an arc and crashed into the cliff. It ended up hanging inverted. The pilot was critically injured and died of his injuries the next day. There was no fire. The emergency locator transmitter (ELT) broke out of its mount and was ejected from the helicopter, where it emitted a signal for about 15 hr.

Accident site
Accident site

Analysis
Because there was no evidence of progressive failure or weather-related problems, this analysis will focus on helicopter operations and systems.

The hard landing of the load is consistent with the helicopter sinking rapidly as it slowed and due to limited performance as predicted in the hover out of ground effect (HOGE) chart.

The pilot may have attempted to correct a nose-down pitch if the helicopter was forward of the load when a large collective input was made. This would explain why there were indications that the cyclic was in the full aft position.

The main rotor blades struck the tail boom in a flight regime (hover) where contact is highly unlikely. The deck support did not break as an initiating factor, and because the tail boom did not break before it was hit, there had to be some other abnormal event to bring the main rotor in contact with the tail boom.

There are a limited number of events that can cause a main rotor to strike the tail boom, but only collective bounce is able to generate the divergence necessary to bring this about under the accident circumstances:

  • The drop of the load (3 ft) onto the drill deck would initiate a bounce.

  • The pilot was leaning out the right door with his left arm extended fully to reach the collective stick (susceptible to an uncommanded movement from a bounce).

  • While the lack of built-in friction could have been mitigated by the pilot applying friction, this was not done and the collective did not serve to help dampen the pilot’s arm movement after the initiating bounce.

  • The longline stretch aggravated vertical movement of the load (bounce).

  • The main rotor blade was flexing down when the helicopter was hovering (divergent vertical movement).

  • Although the load was very heavy for the helicopter, it dropped and rose quite quickly (disproportionate to the normal collective movement), indicating uncommanded power changes.

Therefore, collective bounce likely caused the main rotor to strike the tail boom, probably in the early stages of the divergent vertical movements.

Close-up of aircraft at accident site
Close-up of aircraft at accident site

Findings as to causes and contributing factors

  1. The helicopter was operating at a weight that, when forward speed was reduced, caused it to descend rapidly and the load to hit the drill deck hard. The hard landing of the load, combined with the pilot’s body position, longline stretch, and low collective friction initiated collective bounce, causing the main rotor blades to strike the tail boom.

  2. The tail rotor drive and anti-torque control were lost, causing the helicopter to spin about its yaw axis due to high engine torque; the pilot lost control and the helicopter collided with terrain.

Findings as to risk

  1. Longlines that stretch have been known to induce vertical oscillations and there is a risk of these oscillations accelerating to a point beyond the pilot’s control.

  2. While most helicopter flight manuals contain performance charts, they are often not included in the limitations section and can, therefore, be interpreted as guidance material. There is a risk that not adhering to these performance charts will result in damage to the helicopter, loss of control, or both.

  3. Operating with an unrestrained upper body and without a door increases the risk of injury in the event of an accident.



TSB Final Report A08O0233—Uncontrolled Descent into Terrain

On the night of August 31, 2008, a private pilot rented a Cessna 172P. The pilot and two passengers flew from Brampton Airport, Ont., to Toronto/Buttonville Municipal Airport, Ont., then to Barrie-Orillia (Lake Simcoe Regional) Airport, Ont., and Wiarton Airport, Ont., stopping briefly at each of these locations before beginning a return flight to Brampton. At approximately 04:32 Eastern Daylight Time (EDT) on September 1, 2008, the airplane struck the ground at 44°03’N 080°21’W, approximately 7 NM west of Shelburne, Ont., and was destroyed. There was no fire. Impact damage rendered the emergency locator transmitter (ELT) inoperative. The rear-seat passenger notified emergency services of the accident by cellular telephone, but emergency services were unable to locate the accident site until approximately 06:30 EDT when a local resident found and reported it. The rear-seat passenger was taken by ambulance to a local hospital, examined, and released. The pilot and front-seat passenger were airlifted to a Toronto hospital where the front-seat passenger succumbed to his injuries four days later.

Analysis
In this occurrence, weather was suitable for the flight and was not considered a factor. There was no indication of a mechanical failure of the airplane or of onboard navigation equipment or facilities external to the airplane that may have influenced the events. Therefore, the investigation focused on the pilot and passengers.

The occurrence took place at the lowest point of circadian alertness and after the pilot had likely been awake for 22 consecutive hours. The pilot was therefore at high risk of falling asleep involuntarily: he was very high on the homeostatic scale of propensity for sleep, and he was at the lowest point of the circadian cycle for alertness. The pilot was tasked with maintaining the airplane in a constant direction and altitude at night, a task that is both monotonous and that requires sustained attention. The cockpit environment was one of sustained low-frequency noise and constant consistent vibration.

All on board were accustomed to sleeping at night and were experiencing the lowest point on the circadian rhythm of alertness making them all susceptible to the effects of fatigue. The rear-seat passenger was asleep after leaving Wiarton.

The flight path change that was detected by analysis is consistent with the pilot ceasing to maintain the lateral-directional control input required to maintain the heading of the airplane. As the airplane deviated from its initial azimuth and bank condition, its natural stability would result in a rate of descent that increased as the bank increased, characteristic of spiral mode stability without pilot intervention. The flight path analysis determined that, without any pilot control input, the airplane would continue to fly a descending spiral flight path from the last recorded position on radar to the point where it struck the ground. Furthermore, the analysis predicted accurately the location, heading, and attitude of the airplane at impact.

Final flight path of the C-172
Final flight path of the C-172

The flight path study cannot prove that the persons on board were all asleep, only that they did not intervene in the flight of the airplane during the last 7 min of flight. However, the investigation concluded that, as a result of fatigue, both passengers were sleeping and the pilot involuntarily fell asleep while performing the monotonous task of maintaining straight-and-level flight, after which the airplane reverted to its trimmed condition and continued to fly until it struck the ground.

In the absence of any direct method of measuring an individual’s level of fatigue or propensity for sleep, the defence against fatigue-related accidents is to avoid placing the operation at risk in the first place. In commercial operations, this is accomplished by means of regulatory and operational measures that limit the flight and duty time of flight crews. For individual owners and rental pilots, the sole defence against fatigue is their own judgment, which has been acknowledged to be unreliable since fatigued individuals are typically the poorest judges of their condition. There is no regulatory requirement for flight training units (FTU), flying clubs, or rental operations to exercise the same operational control measures that apply to commercial operations, even though such measures could help reduce risks for affected individuals.

There was a delay in locating the accident site. The pilot did not file a flight plan or flight itinerary; therefore, there was no indication that the airplane was overdue. Although impact forces were of sufficient magnitude, it is possible that the force component along the axis of sensitivity was insufficient to trigger the single-axis inertia switch and activate the ELT. Moreover, the ELT was released from its mounting bracket during impact, and the power source detached, which would have caused the ELT to stop transmitting. As a result, no ELT signals were detected. The physical installation standards for these ELTs do not preclude use of the mechanism by which the retaining strap released the ELT. The design of the over-centre retaining strap for ELTs creates a risk that the ELT will not function in a similar accident.

The airplane’s gross take-off weight exceeded the limitations published in the aircraft flight manual (AFM). As a result, the structural integrity of the airplane and its performance capabilities were not reflected in the AFM. Although these elements did not contribute to the accident, operating an airplane outside its certified limitations incurs a risk that the operator cannot assess.

Aerial view of accident scene
Aerial view of accident scene

Findings as to causes and contributing factors

  1. Due to fatigue, the pilot involuntarily fell asleep resulting in the airplane continuing to fly in its trimmed condition until it struck the ground.

  2. The two passengers, both with flying experience, were asleep and did not identify the developing situation and, therefore, could not alert the pilot.

Findings as to risk

  1. Reliance on a pilot’s own judgment to prevent fatigue-related accidents is an ineffective defence mechanism.

  2. The pilot did not file a flight plan or flight itinerary. As a result, there was no alert that the airplane was overdue, which could delay the initiation of search and rescue efforts.

  3. The pilot utilized a weight and balance worksheet for a different airplane model. As a result, the flight was flown at a gross weight that exceeded the limitations set out in the AFM.

  4. Although it complies with existing standards, the over-centre retaining strap that mounts the ELT to the airplane can release the ELT when subjected to the right combination of impact forces, rendering it inoperable and increasing the risk of delay in locating a crash site.

  5. Although it complies with existing standards, an ELT with a single-axis inertia switch may not be triggered by impact forces in some instances, increasing the risk of delay in locating a crash site. 

Blackfly Air

Click on image to enlarge.

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