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 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 A09W0021—Loss of Power and Collision with Terrain

On January 30, 2009, a Robinson R44 helicopter was en route from Grande Prairie, Alta., to Grande Cache, Alta., with one pilot and one passenger on board. At approximately 17:02 Mountain Standard Time (MST), while climbing over rising terrain, the helicopter lost engine power and main rotor RPM. The pilot turned downhill in an effort to regain main rotor RPM. When this failed, he carried out a forced landing into the trees where the aircraft came to rest on its right side. The pilot was seriously injured when the passenger fell on top of him during impact. The passenger sustained no injury. They spent more than 15 hr on site before being rescued. The emergency locator transmitter (ELT) did not activate during the impact sequence, thus delaying the search and rescue (SAR) response.

Analysis

The weather at the time of the accident was conducive to the formation of carburetor icing. The pilot had spent most of his career flying turbine-powered helicopters, in which carburetor icing is not a concern. The carburetor heat lever can move away from the required position through movement of the collective arm in flight. The reported loss of power was likely the result of carburetor icing, which could not be corrected by the pilot in the time available.

The different SPOT satellite GPS messenger functions activated by the passenger, coupled with uncertainty among family members during discussions with the joint rescue coordination centre (JRCC), contributed to the delay in the SAR response.

The lack of a common communication frequency among SAR responders also contributed to the delay in rescue. Faster clarification of the accident location and coordination of tasks would have shortened rescue time. The risk of serious injury and death increases as SAR response time increases.

Finding as to causes and contributing factors

  1. It is likely that carburetor ice formed resulting in the loss of engine power and main rotor RPM from which the pilot was unable to recover.

TSB Final Report A09O0207—Collision with Terrain

On September 21, 2009, a Robinson R22 Alpha helicopter departed Toronto City Centre Airport, Ont., on a short flight to the pilot’s private helipad in the rural town of Norval, Ont. At 20:00 Eastern Daylight Time (EDT), in the hours of darkness, the helicopter crashed 1.8 NM northeast of the final destination. The helicopter erupted into flames on impact and was partially consumed by a post-crash fire. The pilot was fatally injured.

Analysis

Examination of the helicopter engine indicates that it was not running on impact and that the helicopter struck the ground in a 50° nose-down attitude, suggesting an in-flight loss of control. Although the helicopter was extensively damaged, there were no signs of any pre-impact mechanical failure or system malfunction that could have contributed to this accident. As a result, this analysis focuses on possible scenarios for what caused the engine to stop running and why the helicopter departed controlled flight and collided with terrain.

While it was not possible to determine accurately the position of the carburetor heat control before impact, the mixture control knob was found out and bent. With the push-button locking feature, it is unlikely that the mixture control moved during the impact. It was, therefore, likely in the idle cut-off position on impact.


Centre pedestal with mixture control (upper right) and carburetor heat control (lower right)

Two scenarios were considered as to why the pilot inadvertently pulled the mixture control to the idle cut-off position, causing the engine to shut down:

  • On approaching destination and in preparation for descent, the pilot attempted to apply carburetor heat.
  • The meteorological conditions were conducive to moderate carburetor icing during cruise and descent. The Robinson R22 governor can easily mask carburetor icing by automatically increasing the throttle to maintain engine RPM, which will also result in a constant manifold pressure. It is possible that the helicopter’s engine developed carburetor ice en route, causing performance degradation or a total power loss. To correct this situation, the pilot would have attempted to apply carburetor heat.

The mixture control knob is shaped differently than the carburetor heat knob. To reposition the mixture control, the pilot needs to action the push-button locking feature. In addition, to prevent its inadvertent actuation, the manufacturer also requires that a cylindrical plastic guard be placed over the mixture control knob from the time the engine is started until such time as the engine is shut down. This plastic guard would make it difficult to inadvertently action the mixture control and would also provide tactile feedback that the pilot was attempting to move the wrong control knob. In order for the pilot to be able to pull the mixture control knob to the idle cut-off position, it is likely that the plastic guard had not been placed over the mixture control knob as required.

Mixture control pushed in to full rich with guard installed
Mixture control pushed in to full rich with guard installed

Mixture control pulled out to idle cut-off with guard removed
Mixture control pulled out to idle cut-off with guard removed

In the Robinson R22, the pilot must take immediate action following a loss of power to ensure that rotor RPM is maintained. Failure to do this can lead to a low rotor RPM and rotor stall from which recovery may not be possible. The Robinson R22 pilot operating handbook (POH) emergency procedures for a power loss above 500 ft in part instructs the pilot to immediately lower the collective to maintain rotor RPM and enter a normal autorotation. A restart may be attempted at the pilot’s discretion if sufficient time is available. If unable to restart, the pilot should turn off unnecessary switches and shut off the fuel.

Approximately 40 s before the crash, the helicopter started to turn to the right, then immediately started turning sharply to the left and climbed 300 ft. Approximately 20 s before the crash, the helicopter began a rapid descent from 1 800 ft above sea level (ASL) to the crash site at 650 ft ASL; this equates to a descent rate of approximately 3 450 ft/min. According to Robinson Helicopter Company Safety Notices SN-18 and SN-26, helicopters have less inherent stability and much faster roll rates than airplanes. Loss of the pilot’s outside visual references, even for a moment, can result in spatial disorientation, wrong control inputs and an uncontrolled crash.

With a lack of visual reference at night, limited visibility due to weather and the pilot’s relative inexperience, the pilot likely became spatially disoriented while dealing with the power loss emergency. Unable to determine the correct attitude of the helicopter without visual reference, the pilot lost control, resulting in uncontrolled flight into the terrain.

Findings as to causes and contributing factors

  1. It is likely that, while attempting to apply carburetor heat, the pilot inadvertently pulled the mixture control knob to the idle cut-off position, causing the engine to shut down.
  2. It is likely that the plastic guard had not been placed over the mixture control knob, resulting in the pilot being able to pull the control to the cut-off position.
  3. Following the engine shutdown, the rotor RPM was allowed to decay, resulting in a loss of control and uncontrolled flight into the terrain.
  4. With few visual references, the pilot likely became spatially disoriented, contributing to the inability to maintain control.

Other findings

  1. The helicopter was being operated in Canada without liability insurance as required by the Canadian Aviation Regulations (CARs).
  2. The helicopter had not been registered in Canada as required by the CARs.

TSB Final Report A09P0397—Loss of Control—Collision with Water

Note: The TSB investigation into this occurrence resulted in a major report, with extensive discussions, analysis and recommendations on emergency egress from floatplanes and the wearing of personal floatation devices. Therefore we could only publish selected parts of the report in the ASL. Readers are invited to read the full report, hyperlinked in the title above. —Ed.

On November 29, 2009, a de Havilland DHC-2 MK 1 was departing Lyall Harbour, Saturna Island, B.C., for the water aerodrome at the Vancouver International Airport, B.C. After an unsuccessful attempt at taking off downwind, the pilot took off into the wind towards Lyall Harbour. At approximately 16:03 Pacific Standard Time (PST), the aircraft became airborne, but remained below the surrounding terrain. The aircraft turned left, then descended and collided with the water. Persons nearby responded immediately; however, by the time they arrived at the aircraft, the cabin was below the surface of the water. There were eight persons on board—the pilot and an adult passenger survived and suffered serious injuries; the other six occupants drowned inside the aircraft. No signal from the emergency locator transmitter (ELT) was heard.

Analysis

The DHC-2 Beaver was originally certified without a stall warning system. One had been installed on the occurrence aircraft, but was later rendered unserviceable. The absence of a functioning stall warning system, coupled with the known benign stalling characteristics of the Beaver, precluded any warning of an impending stall. Furthermore, the stall warning horn had been filled with silicone to make it less noisy. It is therefore possible that a horn would not be heard during periods of loud engine noise, thereby increasing the risk of inadvertent stalls.

The conditions in Lyall Harbour at the time of the occurrence were conducive to the development of mechanical turbulence and mountain waves. The turbulence associated with these phenomena likely contributed to vertical gusts, which subjected the aircraft to temporary, but significant, increases in aerodynamic load.

Following takeoff, after the initial climb, the pilot commenced a left turn out of the harbour. The aircraft encountered down flowing air, restricting its ability to gain altitude. As the aircraft turned, it drifted towards terrain, causing the pilot to increase the bank angle. To maintain altitude while banking, the pilot likely had to increase the angle of attack, thereby increasing the load factor and the speed at which the aircraft would stall. While the use of flap may have increased the wing area and consequently decreased its loading, it was likely insufficient to counteract the combined loads brought about by the atmospheric conditions and increase in bank.


Lyall Harbour with flight route and winds

A float-equipped Beaver with the flaps set in the landing position was demonstrated to stall in straight and level flight at 54 mph. In this occurrence, the combined effects of the reduced airspeed during the climb, the bank angle during the turn and the atmospheric conditions increased the load factor of the aircraft to the point of aerodynamic stall.

The aircraft was under its maximum gross takeoff weight, but loaded such that its centre of gravity (CG) was beyond the aft limit for floatplane operations. The aircraft levelled off prior to impact, indicating the pilot had initiated stall recovery.

Full recovery was compromised by the aft CG. Controllability notwithstanding, the altitude from which recovery was made was insufficient to arrest the descent, causing the aircraft to strike the water.

The damage to the pilot’s seat rendered the restraint system ineffective and contributed to the pilot’s injuries. These injuries, which included a brief loss of consciousness, caused a delay in the pilot’s egress and limited his ability to provide assistance to the passengers.

With the exception of one adult, all passengers undid their seatbelts, indicating that they likely remained conscious after impact. Following the impact, the passengers would have had a few seconds to locate a suitable egress point, release their seat belts and exit the aircraft.

In this occurrence, the aircraft was not equipped with jettisonable doors or windows. As a result, the only possible egress points were the four doors on the aircraft. However, impact damage jammed two of the four doors and restricted egress from the sinking aircraft, which meant all seven passengers and the pilot would have had to exit via one of two usable egress points. Rather than deliberately attempting to open a door, the surviving passenger exited through the door that had opened as a result of impact forces. It is likely that the pilot’s recent egress training contributed to him being able to open the door and escape from the aircraft. The lack of alternate emergency exits, such as jettisonable windows, increases the risk that passengers and pilots will be unable to escape a submerged aircraft due to structural damage to primary exits following an impact with the water.

Seeing as the impact forces experienced by all onboard were considered survivable, the issue of timely escape contributed to the passengers drowning. Many persons could improve their chances of survival by identifying the possible exits and mentally rehearsing their actions, including identifying alternate exits in the event of an accident. If passengers are not provided with explicit safety briefings on how to egress the aircraft when submerged, there is increased risk that they will be unable to escape following an impact with the water.

Given the time involved in conducting a rescue, in cases when an individual is successful in escaping an aircraft following an impact, continued survival is a significant concern. This is particularly true if the individual has been injured. Since it is unlikely that persons faced with the urgency of escape in water will retrieve life vests stored in the aircraft, passengers and pilots not equipped with some type of flotation device prior to an impact with the water are at increased risk of drowning once they have escaped the aircraft.

Findings as to causes and contributing factors

  1. The combined effects of the atmospheric conditions and bank angle increased the load factor, causing an aerodynamic stall.
  2. Due to the absence of a functioning stall warning system, in addition to the benign stalling characteristics of the Beaver, the pilot was not warned of the impending stall.
  3. Because the aircraft was loaded in a manner that exceeded the aft CG limit, full stall recovery was compromised.
  4. The altitude from which recovery was attempted was insufficient to arrest descent, causing the aircraft to strike the water.
  5. Impact damage jammed two of the four doors, restricting egress from the sinking aircraft.
  6. The pilot’s seat failed and he was unrestrained, contributing to the seriousness of his injuries and limiting his ability to assist passengers.

Findings as to risk

  1. There is a risk that pilots will inadvertently stall aircraft if the stall warning system is unserviceable or if the audio warnings have been modified to reduce noise levels.
  2. Pilots who do not undergo underwater egress training are at greater risk of not escaping submerged aircraft.
  3. The lack of alternate emergency exits, such as jettisonable windows, increases the risk that passengers and pilots will be unable to escape a submerged aircraft due to structural damage to primary exits following an impact with the water.
  4. If passengers are not provided with explicit safety briefings on how to egress the aircraft when submerged, there is increased risk that they will be unable to escape following an impact with the water.
  5. Passengers and pilots not wearing some type of flotation device prior to an impact with the water are at increased risk of drowning once they have escaped the aircraft.

Safety action taken

Operator

The operator has equipped each aircraft with hand-held baggage scales to allow pilots to make more accurate weight and balance calculations.

The operator has ordered new door latch release and window modification kits from Viking Air Limited, the aircraft type certificate holder.

The operator has enhanced its pre-flight safety briefing by now including an independent demonstration of where to find the life vests, what they look like and how to put them on. A mannequin located at the operator’s Vancouver and Nanaimo docks is used to perform this safety demonstration. Enlarged photographs from the safety briefing cards are displayed on the mannequin stand. A briefing is provided to passengers before they head down to the aircraft at the dock and a second safety briefing is provided once they are at the aircraft.

Viking Air Limited

Viking Air Limited, the aircraft type certificate holder, has made push-out window and cabin and cockpit door latch kits available for installation on Beaver aircraft.

Transport Canada

Since this accident, Transport Canada (TC) completed a number of initiatives:

  • TC facilitated a meeting of floatplane operators in October 2010, which resulted in the formation of an industry-led safety association of B.C. floatplane operators.
  • TC ran an updated floatplane safety promotional campaign during the summer of 2011, which included:
    • publishing articles in the Aviation Safety Letter to promote egress training and effective passenger briefings;
    • developing posters and pamphlets for distribution to floatplane passengers to increase awareness of their role in safety;
    • tasking its inspectors to ensure floatplane operators receive the latest safety promotion materials, to emphasize the importance of egress training and better passenger briefings during their visits, and to conduct follow-up telephone surveys of floatplane operators to verify that they are using the safety promotion materials;
    • developing a Web portal to centralize floatplane safety information for use by operators and passengers and encouraging floatplane operators to provide a link to the portal from their Web sites;
    • producing a video for use by operators promoting best practices and lessons learned in floatplane operations; and
    • producing a video for use by floatplane passengers on their role in safety.
  • TC issued a Civil Aviation Safety Alert (CASA) on June 6, 2011, with its focus on commercial and private floatplane operators and pilots, recommending the following best practices in relation to floatplane safety:
    • Upper body restraints to be used by front seat occupants;
    • Passenger briefings on the proper usage of floatation devices during emergency egress;
    • Underwater emergency egress training for flight crew; and
    • Aircraft safety design improvements facilitating egress.

TSB Final Report A09Q0203—Controlled Flight into Terrain (CFIT)

Note: The TSB investigation into this CFIT occurrence resulted in a major report, with extensive discussions, analysis and recommendations on instrument approach design, instrument approach depiction, instrument approach techniques, approach and landing accidents, and approach and landing accident reduction (ALAR) initiatives. Therefore we could only publish the summary, findings and some of the safety actions in the ASL. Readers are invited to read the full report, hyperlinked in the title above. This occurrence report also prompted the publication of the article on the Flight Safety Foundation’s (FSF) ALAR Tool Kit in this issue of the ASL. —Ed.

On December 9, 2009, a Beech A100 was on an instrument flight rules (IFR) flight between Val-d’Or, Que., and Chicoutimi/ Saint-Honoré, Que., with two pilots and two passengers on board. At 22:40 Eastern Standard Time (EST), the aircraft was cleared for an RNAV (GNSS) Runway 12 approach and switched to the aerodrome traffic frequency. At 22:50 EST, the International satellite system for search and rescue detected the aircraft’s emergency locator transmitter (ELT) signal. The aircraft was located at 02:24 EST in a wooded area approximately 3 NM from the threshold of Runway 12, on the approach centreline. Rescuers arrived on the scene at 04:15 EST. The two pilots were fatally injured, and the two passengers were seriously injured. The aircraft was destroyed on impact; there was no post-crash fire.

Aircraft wreckage
Aircraft wreckage

Finding as to causes and contributing factors

  1. For undetermined reasons, the crew continued its descent prematurely below the published approach minima, leading to a controlled flight into terrain (CFIT).

Findings as to risk

  1. The use of the step-down descent technique rather than the stabilized constant descent angle (SCDA) technique for non-precision instrument approaches increases the risk of an approach and landing accident (ALA).
  2. The depiction of the RNAV (GNSS) Runway 12 approach published in the Canada Air Pilot (CAP) does not incorporate recognized visual elements for reducing ALAs, as recommended in Annex 4 to the Convention on International Civil Aviation, thereby reducing awareness of the terrain.
  3. The installation of a terrain awareness warning system (TAWS) is not yet a requirement under the Canadian Aviation Regulations (CARs) for air taxi operators1. Until the changes to the regulations are put into effect, an important defense against ALAs is not available.
  4. Most air taxi operators are unaware of and have not implemented the FSF ALAR Task Force recommendations, which increases the risk of a CFIT accident.
  5. Approach design based primarily on obstacle clearance instead of the 3° optimum angle increases the risk of ALAs.
  6. The lack of information on the SCDA technique in Transport Canada reference manuals means that crews are unfamiliar with this technique, thereby increasing the risk of ALAs.
  7. Use of the step-down descent technique prolongs the time spent at minimum altitude, thereby increasing the risk of ALAs.
  8. Pilots are not sufficiently educated on instrument approach procedure design criteria. Consequently, they tend to use the CAP published altitudes as targets, and place the aircraft at low altitude prematurely, thereby increasing the risk of an ALA.
  9. Where pilots do not have up-to-date information on runway conditions needed to check runway contamination and landing distance performance, there is an increased risk of landing accidents.
  10. Non-compliance with IFR reporting procedures at uncontrolled airports increases the risk of collision with other aircraft or vehicles.
  11. If altimeter corrections for low temperature and remote altimeter settings are not accurately applied, obstacle clearance will be reduced, thereby increasing the CFIT risk.
  12. When cockpit recordings are not available to an investigation, this may preclude the identification and communication of safety deficiencies to advance transportation safety.
  13. Task-induced fatigue has a negative effect on visual and cognitive performance, which can diminish the ability to concentrate, operational memory, perception and visual acuity.
  14. Where an ELT is not registered with the Canadian Beacon Registry, the time needed to contact the owner or operator is increased, which could affect occupant rescue and survival.
  15. If the tracking of a call to 9-1-1 emergency services from a cell phone is not accurate, search and rescue efforts may be misdirected or delayed, which could affect occupant rescue and survival.

Other findings

  1. Weather conditions at the alternate airport did not meet CARs requirements, thereby reducing the probability of a successful approach and landing at the alternate airport if a diversion became necessary.
  2. Following the accident, none of the aircraft exits were usable.

Safety action taken

Operator

To minimize the risks of ALAs, the operator implemented SCDA in its standard operating procedures (SOPs).

A program was set up to progressively install radio altimeters on the company aircraft.

The company CFIT training was reviewed to integrate the recommendations of the FSF ALAR Task Force.

The following measures have been, or will be, taken by the operator to reduce the operational risks:

  • A review of all departments related to flight operations.
  • A complete review of SOPs.
  • A review of operational limitations of the charter operations (i.e. new restrictions for new captains and first officers as well as equipment restrictions).
  • All flying personnel will redo the company CFIT course.
  • A risk analysis file is available to the flight crew to review the level of risk associated with approaches in instrument meteorological conditions (IMC) for all destinations. This file is based on the FSF program.
  • A flight safety awareness campaign called “Objectif Zéro” was set up to involve all company employees. The aim is to allow all employees to have a positive impact on flight safety via the company safety management system (SMS).

Decorative line

1 On July 4, 2012, Transport Canada announced new regulations requiring the installation and operation of TAWS in private turbine-powered and commercial airplanes configured with six or more passenger seats. The regulatory amendments introduce requirements for the installation of TAWS equipped with an enhanced altitude accuracy (EAA) function. Most current TAWS equipment include this function; however, operators who have previously installed older TAWS models may not have equipment with this functionality. Operators have two years from the date the regulations came into force to equip their airplanes with TAWS and five years to equip with EAA.

Decorative line

TSB Final Report A10P0147—Loss of Control—Collision with Water

On May 29, 2010, a float-equipped Cessna 185F took off from Tofino, B.C., at 12:00 Pacific Daylight Time (PDT) for a flight to Ahousat, B.C., with a pilot and three passengers. The short flight was being carried out under visual flight rules (VFR) at about 500 ft above sea level (ASL). About 2 NM from Ahousat, while in cruise flight, the aircraft descended in a steep nose-down attitude until it hit the water in Millar Channel and overturned. Attempts to secure the aircraft failed and it sank. There were no survivors. The emergency locator transmitter (ELT) functioned but its signal was not received until the wreckage was brought to the surface two days later.

Analysis

The weather was suitable for the VFR flight; the wind direction and speed would not have caused downdrafts or severe turbulence on the flight route. There was no evidence to suggest that any mechanical or environmental issue played a role in this occurrence.

The aircraft struck the water at an angle and speed consistent with a deliberate dive, or a loss of control. Based on the pilot’s demeanour, there was no reason to dive to the point of impact with the water. Therefore, the TSB concluded that the pilot lost control of the aircraft.

The aircraft was trimmed for level cruising flight. Had the pilot simply released the controls, the aircraft would have remained more or less in level cruising flight, and it would not have pitched down abruptly or to an angle of 45°. To sustain a descent at a 45° angle from level attitude, a high and continued pressure would have had to have been placed on the control column.

The passengers were intoxicated at the time they boarded the aircraft, and had previously been argumentative. The final location of some beer cans and fragments of the beer case indicate that the case of beer was in proximity to the passengers just before impact.

It is not known if all the passengers were wearing their seat belts at the start of the flight, but the physical evidence shows that the seatbelts of the passenger in the right front seat (beside the pilot) and of the passenger in the left rear seat (behind the pilot) were not fastened at impact.

What was happening in the cabin moments before the pilot lost control cannot be accurately determined. However, the TSB concluded that this probably involved activity by the unsecured passengers that interfered with the pilot and his control of the aircraft.

The pilot’s broken right wrist and the bent V brace suggest that the pilot was bracing or trying to resist a force imposed from behind. The broken ankles of the passenger behind the pilot are consistent with that person bracing with both feet, or pushing forward with both feet, at the time of impact. It is possible the passenger seated behind the pilot kicked the pilot’s seatback forward and held it there, pushing the pilot into the instrument panel and the controls forward, thereby inducing a dive.

Because there was no locking mechanism on the pilot’s seatback, and because the pilot was not wearing his shoulder strap, he would have been unable to prevent his upper body from being forced onto the instrument panel.

When aircraft controls are accessible to passengers there is a risk of inadvertent control manipulation and a risk of the pilot losing control of the aircraft at a critical time of flight operations.

It is also possible the level of the passengers’ intoxication impaired their ability to recognize the gravity of the situation and stop their interference in time for the pilot to regain control of the aircraft before impact.

Findings as to causes and contributing factors

  1. It is likely that passenger interference caused the pilot to lose control of the aircraft, whereupon it descended in a steep nose-down attitude until it struck the water.
  2. It is possible the passengers’ level of intoxication contributed to their inability to recognize the gravity of the situation and stop the interference in time for the pilot to regain control of the aircraft before impact.
  3. Because there was no locking mechanism on the pilot’s seatback, and because the pilot was not wearing his shoulder strap, he would have been unable to prevent his upper body from being forced onto the instrument panel.

Findings as to risk

  1. When controls are accessible to passengers there is a risk of inadvertent control manipulation and a risk of the pilot losing control of the aircraft.
  2. When upper body restraint systems are not used, there is a risk of serious head injury in the event of an accident.
  3. When cargo or passengers’ baggage is not restrained, there is a risk of unsecured items injuring persons on board in the event of sudden aircraft stoppage or encounters with severe turbulence.

Other finding

  • Post-impact survival issues such as egress and flotation were not relevant in this accident.

Safety action taken

British Columbia Coroners Service

The British Columbia Coroners Service has made the following recommendation to Transport Canada as a result of its investigation into the deaths of the four individuals:

It is recommended that all commercial air operators be required to establish a policy, procedure, and training (based on the Canadian [Aviation] Regulations) for all personnel, to assist them in identifying inappropriate behaviour in passengers, and take the necessary action to mitigate risk where there are reasonable grounds to believe that the person’s faculties are impaired by alcohol or drugs.

This recommendation is currently under review by Transport Canada officials. In the meantime, we strongly encourage all operators to review CAR 602.4 Alcohol or Drugs – Passengers.

TSB Final Report A10Q0218—Engine Failure and Hard Landing

On December 9, 2010, a Bell 206B, equipped with high skid landing gear, departed Matane, Que., on a visual flight rules (VFR) flight with the pilot and four passengers on board. The aircraft was flying northeast at low altitude over the south shore of the Saint Lawrence River so that the passengers could evaluate and document damage caused by high tides. At 11:31 Eastern Standard Time (EST), approximately 27 min after takeoff, the helicopter experienced an engine (Rolls-Royce 250-C20B) failure. The pilot did an autorotation with a right turn of more than 180°. The aircraft landed hard on the beach, breaking the landing gear, and came to rest on its belly. One of the occupants was seriously injured, two had minor injuries and two were unharmed in the accident.

Analysis

The No. 2 bearing assembly in the engine broke down due to the fatigue failure of its cage. Because this bearing served as a thrust bearing, its failure caused the compressor to move forward, which in turn brought the impeller into contact with the shroud. The resulting friction led to significant deceleration and a loss of power. The propulsive movement of the compressor caused it to stall, as demonstrated by the bangs it produced.

The breaking of a gearbox stud, the crack in the compressor scroll and the fatigue failure of three fingers in the vibration damper may suggest that the damage was caused by abnormal engine vibration. However, after the stud and scroll were repaired, the engine was tested on a test bench, and no anomalies or vibrations outside of the limit were noted. This suggests that it is unlikely that engine vibration caused the anomalies. It can also be concluded that the vibration damper was not fractured at the time of the inspection on the test bench. Consequently, the successive fractures of the damper fingers occurred during the last 30 flight hours.

Because three fingers had fractured less than 30 flight hours before the accident, the vibration damper was less effective. It cannot be concluded beyond all doubt that the broken damper caused the No. 2 bearing assembly to fail. However, the partial failure of a component intended to absorb engine vibration cannot be ruled out; it could have altered the vibration load of the compressor, increasing the load on the No. 2 bearing assembly and causing its cage to sustain a fatigue failure.

Although the gearbox had been disassembled three times less than 35 flight hours before the accident, no anomalies were observed. The ball bearings and the vibration damper were not examined because the disassembly of the gearbox was not meant to verify their condition. Therefore, the engine may have been rebuilt with components that needed to be replaced.

The engine was equipped with a working chip-detection system, but the pilot did not notice the warning light before the loss of power, while significant spalling was generated by the slippage of the ball bearings in the No. 2 bearing assembly. However, 3.2 flight hours before the accident, the chip detectors detected metallic debris in smaller quantities from the engine ball bearings, which were starting to break down. Consequently, the ENG CHIP warning light may have been illuminated without the pilot noticing.

According to the height/speed chart, the loss of power occurred in an operating range within which a safe emergency landing was possible. At the time of the failure, there were three operating conditions posing a greater challenge than usual for the pilot. Given the height of the aircraft, the pilot had little time to lower the collective, perform a 180° turn into the wind, and begin the descent before landing on a slope. The power loss caused a rapid drop in rotor RPM to the point where the low rotor RPM warning horn sounded during the descent. It can be concluded that the collective was off the down stop and that the rotor RPM fell below 90 percent.

Findings as to causes and contributing factors

  1. The No. 2 bearing assembly in the engine broke down due to the fatigue failure of its cage. The failure of the bearing assembly caused the engine to lose power.
  2. The power loss caused a rapid drop in rotor RPM to the point where the LOW ROTOR RPM warning horn sounded during the descent. It can be deduced that the collective was not completely lowered and that rotor RPM dropped below 90 percent. This caused a hard landing.

Findings as to risk

  1. Although the aircraft was operated outside of the high-risk “to avoid” zone on the height/speed chart, the autorotation resulted in a hard landing. Because of operating factors other than speed and height, the operation of the helicopter at low altitude posed a risk to safe landing in the event of an engine failure.
  2. Operating an aircraft outside of the weight and balance limits set by the manufacturer can reduce aircraft performance and cause a power surge, in turn causing major damage to the engine, airframe and power train.
  3. The aircraft can attain the performance figures in the height/speed chart when it is loaded with its limit weight. Operating the aircraft at a higher weight compromises the success of an autorotation following an engine failure.

Other finding

  1. The wear on the ball bearings and the vibration damper was not observed when the gearbox was examined because the three engine teardowns performed within the 31 flight hours before the accident did not expose them and were not intended to verify their condition.

TSB Final Report A10A0122—Controlled Flight Into Terrain

On December 14, 2010, at 19:41 Atlantic Standard Time (AST), a Cessna 310R departed the Montréal/St-Hubert Airport, Que., on a night instrument flight rules (IFR) flight to the Pokemouche Airport, N.B. Between 21:56 AST and 21:58 AST, three transmissions were received from the occurrence aircraft’s 406 MHz emergency locator transmitter (ELT); however, the signal terminated before the location could be determined. The wreckage was located two days later in a wooded area, approximately 5.5 NM west-northwest of the Pokemouche Airport. The aircraft was destroyed by the impact and post-crash fire. The lone occupant was fatally injured.

Analysis

On the day of the occurrence, the departure altimeter setting for St-Hubert was 29.61 in. Hg and the arrival altimeter setting for Bathurst, N.B., was 29.41 in. Hg. If the Bathurst altimeter setting was not applied prior to the commencement of the instrument approach, the aircraft’s actual altitude would have been 200 ft lower than indicated on the altimeter. While an altimeter error of this nature would reduce safety margins, levelling off at the minimum descent altitude with the incorrect altimeter setting of 29.61 in. Hg would still provide several hundred feet of clearance between the aircraft and the terrain. As a result, it is unlikely that the aircraft impacted the ground simply because the altimeter had not been switched to the current Bathurst altimeter setting.

This occurrence involved several of the most common factors associated with controlled flight into terrain (CFIT) accidents. In particular, it involved flight conditions that would make it nearly impossible to see the approaching terrain and it involved an instrument approach procedure with multiple step-down altitudes. As a result, each time that a descent is commenced, the pilot must remain vigilant to ensure that the aircraft does not descend below the appropriate minimum safe altitude, which during this portion of the approach was 1 000 ft above sea level (ASL). The combination of a non-precision instrument approach, conducted at night, with low ceilings and limited visibility significantly increases the risk of CFIT.

The operator was not authorized to conduct GPS approaches on revenue flights, and there was no evidence of the pilot undergoing the required training for conducting GPS approaches. While familiar with the aircraft and operating environment around Pokemouche, the pilot was inexperienced with the newly installed equipment. As a result, trying to use the new and unfamiliar GPS with a terrain awareness feature and audio panel in adverse weather at night would have increased pilot workload and made it difficult to maintain situational awareness. Based on the heading and location of the aircraft at the time of the impact, it is likely that the pilot was attempting to carry out the area navigation (RNAV) approach to Runway 13 and inadvertently flew into terrain.

The pilot elected to return to Pokemouche on the evening of December 14, 2010, so the aircraft would be available for an unexpected charter flight booked for the following morning. This influenced the pilot’s decision to depart, despite the pilot’s lack of familiarity with the new GPS and unfavourable weather at the destination. The pilot, under self-imposed pressure, likely elected to carry out a GPS approach to Runway 13 in IFR weather that was at or below landing limits. The other two approaches available were on Runway 31, both having the same landing limits as the approach to Runway 13.

Currently, there is no requirement for smaller Canadian-registered aircraft to be equipped with terrain awareness and warning systems (TAWS). Although Transport Canada has proposed new regulations which will require TAWS for commercially operated turbine-powered aircraft with six or more passenger seats, the regulation will not require TAWS to be installed on commercially operated turbine-powered aircraft with less than six passenger seats. The lack of regulation requiring TAWS on all commercially operated passenger aircraft places flight crew and passengers travelling on those aircraft at increased risk of CFIT.

The occurrence aircraft was fitted with a terrain awareness feature which would visually warn the pilot of the aircraft’s proximity to terrain if it got too low during an instrument approach. This type of equipment is an example of recent advances in technology designed to improve a pilot’s situational awareness and reduce the risk of CFIT. However, in order for its full potential to be realized, pilots must be properly trained in the use of the terrain awareness feature.

In this occurrence, the pilot received a brief familiarization session on the GPS, avionics, and terrain awareness feature that had been newly installed in the aircraft. It is unknown whether the terrain awareness feature was activated during the RNAV approach to Runway 13. It is possible that the terrain awareness feature was activated and that the pilot did not understand the information that was being presented. The lack of adequate training on newly installed equipment, such as a GPS with a terrain awareness feature, increases the risk of improper use during flight.

It took two days for search and rescue (SAR) personnel to locate the aircraft. This is due to the 406 MHz ELT, which was not equipped with GPS encoding, only transmitting briefly before it was rendered inoperative. If 406 MHz ELTs are not GPS-encoded, there is increased risk that SAR services will be delayed unnecessarily if the ELT is rendered inoperative following an occurrence.

Aircraft flight path to Pokemouche Airport
Aircraft flight path to Pokemouche Airport

Findings as to causes and contributing factors

  1. The pilot, under self-imposed pressure to meet an unexpected charter request the next day, likely elected to carry out an RNAV approach in IFR weather that was at or below landing limits.
  2. It is likely that the aircraft was inadvertently flown into terrain while the pilot was attempting to carry out the RNAV approach to Runway 13.
  3. Attempting to use a new and unfamiliar GPS, terrain awareness feature and audio panel in adverse weather at night would have increased pilot workload, making it difficult to maintain situational awareness.

Findings as to risk

  1. The combination of a non-precision instrument approach, conducted at night, with low ceilings and limited visibility significantly increases the risk of CFIT.
  2. The lack of regulation requiring TAWS on all commercially operated passenger aircraft places flight crew and passengers travelling on those aircraft at increased risk of CFIT.
  3. The lack of adequate training on newly installed equipment, such as a GPS with a terrain awareness feature, increases the risk of improper use during flight.
  4. If 406 MHz ELTs are not GPS-encoded, there is increased risk that SAR services will be delayed unnecessarily if the ELT is rendered inoperative following an occurrence.

Other finding

  1. It is unlikely that the aircraft impacted the ground simply because the altimeter had not been switched to the current Bathurst altimeter setting.

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