Sunday, October 22, 2017
Transport Canada - Aviation Safety Letter Recently Released TSB Reports Issue 2/2010

Recently Released TSB Reports Issue 2/2010

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. We encourage our readers to read the complete reports on the TSB Web site. For more information, contact the TSB or visit their Web site at —Ed.

TSB Final Report A06O0231—Collision with Terrain

On September 4, 2006, the pilot of an amateur-built Pitts S1S aerobatic biplane was on a local flight from his private grass airstrip in Melancthon, Ont., when the aircraft struck the ground following a low-level roll. The impact and post-crash fire destroyed the aircraft. The pilot, the only person on board, received fatal injuries. The accident happened at 19:59 Eastern Daylight Time (EDT) during twilight hours.

Image of crash site

The pilot had extensive flight experience and had flown the Pitts S1S for 160 hr over the previous seven years. He was also experienced at flying low-level aerobatics. There was no indication that the roll was anything other than an intentional aerobatic manoeuvre. The fact that the aircraft struck the ground in a wings-level attitude immediately following the completion of a roll indicates that the pilot was probably controlling the aircraft throughout the manoeuvre and that the rudder and aileron control systems were functional.

It could not be determined why the aircraft struck the ground. There were no identifiable problems with the aircraft, the pilot was fit for the intended flight, and the autopsy did not reveal any pre-existing medical conditions that would have contributed to the accident. As well, it was considered that weather did not play a part in the accident. The analysis will therefore focus on physiological aspects of this flight.

The setting sun to the west was bright and would tend to illuminate the countryside in that direction. It was significantly darker to the east, which would make the horizon more difficult to distinguish in that direction.

The pilot departed to the west and completed at least one turn to the east and two 360° turns before beginning the roll manoeuvre on an easterly heading. Each time the pilot turned past the setting sun, his eyes would have been subjected to the bright light of the sun, and each time he headed in an easterly direction, he would have been looking at a relatively dark horizon. Each time the pilot’s eyes were exposed to the bright light, the process of dark adaptation would have had to begin again. Since there is no way to determine where the pilot was looking as he turned toward the setting sun, the amount of dark adaptation required cannot be quantified. However, each time the aircraft turned from west to east, the eastern horizon would have been more difficult to pick up.

Two factors that likely contributed to the accident were the light conditions and the low altitude at which the roll manoeuvre was initiated. The low light conditions would have made it more difficult for the pilot to identify the exact attitude of the aircraft in a dynamic manoeuvre such as a roll. The horizon to the east was darker than the horizon to the north or south. Thus, while it would have been relatively easy to identify that the wings were level, it would have been more difficult to identify whether the nose was in a level-flight attitude. The low altitude is significant because it minimized the amount of time that the pilot had to recognize and correct any errors as he completed the roll. It is probable that the pilot did not recognize that the aircraft was descending and flew it into the ground.

Findings as to causes and contributing factors

  1. As the pilot was completing a roll at low altitude, the aircraft descended. It is probable that the pilot did not recognize that the aircraft was descending and flew it into the ground.

  2. The varying light conditions during manoeuvring could have made it difficult for the pilot to detect that the aircraft was descending.

Finding as to risk

  1. The pilot of the Pitts aircraft flew in close proximity to another aircraft without having discussed his plans with the other pilot.

TSB Final Report A06P0190—Loss of Control— Transmission Pylon Support Spindle Fracture

On September 19, 2006, at about 07:10 Pacific Daylight Time (PDT), a Bell 206B helicopter, with one pilot and two passengers on board, departed from a service landing area about 0.5 NM from the village of Alice Arm, B.C. The flight was conducted under visual meteorological conditions (VMC). This was the first flight of the day, and the pilot was conducting a crew change at a resource-exploration drill site about 6 NM to the north. The flight departed on a northeast heading across the tidal estuary in front of the village and crashed in the estuary 0.5 NM from the departure point. It was low tide at the time. The helicopter was destroyed, and all three persons on board were fatally injured. There were indications of a small post-impact fire that self-extinguished. There were no eyewitnesses.

Examination of the ground scars and photographs taken before the wreckage was moved revealed a wreckage distribution pattern associated with a condition of high deceleration forces and a steep angle of descent to the level ground, which are consistent with a loss of control. Weather, pilot incapacitation, and engine failure were assessed as unlikely contributors; the investigation focused on flight control malfunction/failure.

The observations made during testing with the Bell 206B static display demonstrated that damage around the main transmission was consistent with the misalignment of the pylon assembly in flight. Although the main driveshaft and pylon assembly were misaligned, the main rotor and tail rotor were still being driven by the engine until the time of impact.

The right-hand pylon support spindle was found fractured at the root end of the journal section, yet the spherical bearing supporting the spindle did not display impact-related damage. This indicates that the right-hand pylon support spindle was not in the spherical bearing at the time of impact. A fatigue fracture is not consistent with an impact force. The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle.

Testing with the Bell 206B static aircraft also demonstrated that the cyclic and collective control linkages could partially support the fuselage from the swash plate assembly, and this condition would render the helicopter uncontrollable in flight, regardless of pilot inputs. It is likely that the time between the spindle failure and ground impact could be measured in seconds. If the helicopter had flown for any longer, any uncontrolled gyrations that may have occurred would likely have resulted in the helicopter breaking apart in flight. Since the accident site was compact, it is more likely that the helicopter was at a low altitude and collided with the ground before time allowed it to break up in flight.

Exemplar pylon support spindle
Exemplar pylon support spindle

Exemplar pylon support spindle
Exemplar pylon support spindle

Findings as to causes and contributing factors

  1. The dimensional restoration repair of the spindle journal introduced a stress concentration feature at the location of the subsurface radius, which was responsible for the formation of the fatigue crack and subsequent failure of the right-hand pylon support spindle.

  2. Failure of the right-hand pylon support spindle in flight caused the helicopter to become uncontrollable and collide with the level ground.

Findings as to risk

  1. It is likely that the pylon-support-spindle repair process was designed without the benefit of all original design data. It could not be shown that tests, stress analyses or other techniques were used to ensure that the repair maintained the strength and other properties assumed in the original design data.

  2. There is a risk that repair designs for parts identified as critical may have been approved before the definition of critical parts, applicable to normal category rotorcraft, was adopted by Transport Canada (TC). Such repair schemes may not ensure that critical parts maintain the critical characteristics on which certification is based.

  3. TC made inquiries regarding approved spindle repair procedures following the release of Bell Helicopter Textron Inc. (BHTI) Operational Safety Notice (OSN) 206-99-35 Revision A, but it closed the file without formally reviewing or cancelling the two approved repair certificates, thus allowing the repair to continue in its original form.

Safety action taken
On February 6, 2007, the TSB issued Occurrence Bulletin OB-A06P0190-1 addressed to TC. The Occurrence Bulletin provided a factual description of the failure mode of the pylon support spindle.

On February 27, 2007, TC issued Airworthiness Directive (AD) CF-2007-02, which mandated removal of all affected Bell 206B pylon support spindles and mandated that maintenance records be annotated accordingly.

On March 9, 2007, BHTI issued OSN 206-99-35 Revision B. This document is a revision of the previous version (Revision A) and reinforces BHTI’s opposition to dimensional restoration repairs of Bell 206B pylon support spindles.

On August 23, 2007, AD CF-2007-02 was superseded and CF-2007-02R1 was issued by TC. The revision included serial numbers of pylon support spindles, which incorporated a similar repair performed by another company.

TSB Final Report A07O0030—Uncontrolled Flight into Terrain

On February 2, 2007, the crew of a Robinson R44 II helicopter was conducting a series of maintenance check flights following a change of the aircraft’s main rotor blades. The pilot and aircraft maintenance engineer (AME) were tasked with “blade tracking”, and the engineer had made pitch link adjustments on the main rotor blades based on the results of two earlier flights. The occurrence flight was conducted with the intention of blade tracking and checking the rotor RPM during an autorotation procedure.

At approximately 17:28 Eastern Standard Time (EST), in low light conditions, the aircraft entered the autorotation at 2 400 ft above sea level (ASL) and continued its descent until it impacted the snow-covered frozen field. The emergency locator transmitter (ELT) activated, and rescue and fire-fighting teams responded. Both occupants suffered serious injuries and were ejected from the cockpit when the seat-belt attachments failed. The aircraft was destroyed.

Image of crash site

The helicopter departed from Cambridge, Ont., on a maintenance test flight. The purpose of the flight was twofold. First, the AME was attempting to track the main rotor blades while the helicopter was in an autorotation and, second, he wanted to check the autorotational RPM. There is a specific procedure in the maintenance manual for checking the autorotational RPM, though it was not reviewed before the flight and was not being followed. Tracking the main rotor blades in an autorotation is not a procedure that is described in the helicopter maintenance manual.

Without a detailed pre-flight briefing, the pilot might not have been fully aware of what to expect during this maintenance test flight. The consequences of not reviewing the autorotational RPM adjustment procedure prior to the flight included not having enough altitude to properly conduct the test and not being aware that, at its current weight, the target rotor RPM was above the main rotor RPM red line.

The flight was normal up to the point where the autorotation was initiated. At some point during the autorotation, the pilot allowed the rotor RPM to drop to approximately 80 percent and was unable to recover before the helicopter hit the ground. The upward bending of the rotor blade confirms that, at some point in the autorotation, the rotor RPM was low. Losing rotor RPM could be the result of incorrect technique when initiating the autorotation, or it could have resulted from a failure to continually monitor the RPM throughout the autorotation.

When the helicopter struck the ground, the rotor tachometer was indicating 98 percent, the rate of descent was 800 ft/min, and the helicopter had very little forward speed. All of this indicates that although full throttle had been reapplied during descent, there was insufficient altitude and time to arrest the descent prior to impact.

Findings as to causes and contributing factors

  1. The AME was attempting to track the main rotor blades while the helicopter was in an autorotation. This procedure was not described in the helicopter maintenance manual. Attempting to combine these two activities likely interfered with the pilot’s ability to monitor aircraft performance during the autorotation.

  2. The gross weight of the helicopter exceeded the maximum specified by the manufacturer for checking rotor RPM in autorotation.

  3. During the autorotation, the rotor RPM decayed to approximately 80 percent and, although full throttle had likely been reapplied, there was insufficient altitude and time remaining to arrest the rate of descent prior to impact.

TSB Final Report A07O0124—Hard Landing and Main Landing Gear Collapse

On May 20, 2007, a Bombardier CL-600-2B19 Regional Jet with 3 crew members and 37 passengers on board, was operating on a flight from Moncton, N.B., to Toronto/Lester B. Pearson International Airport, Ont. At 12:35 Eastern Daylight Time (EDT), the aircraft landed on Runway 06R with a 90º crosswind from the left, gusting from 13 to 23 kt. The aircraft first contacted the runway in a left-wing-down sideslip. The left main landing gear struck the runway first, and the aircraft sustained a sharp lateral side load before bouncing. Once airborne again, the flight and ground spoilers deployed and the aircraft landed hard. Both main landing-gear trunnion fittings failed, and the landing gear collapsed. The aircraft remained upright, supported by the landing gear struts and wheels. The aircraft slid down the runway and exited via a taxiway, where the passengers deplaned. There was no fire. There were no injuries to the crew; some passengers reported minor injuries as a result of the hard landing.

Findings as to causes and contributing factors

  1. On final approach, the captain diverted his attention from monitoring the flight, leaving most of the decision making and control of the aircraft to the first officer, who was significantly less experienced on the aircraft type. As a result, the first officer was not fully supervised during the late stages of the approach.

  2. The first officer did not adhere to the operator’s standard operating procedures (SOPs) in the handling of the autopilot and thrust levers on short final, which left the aircraft highly susceptible to a bounce and without the bounce protection normally provided by the ground lift dump (GLD) system.

  3. Neither the aircraft operating manual nor the training that both pilots had received mentioned the importance of conducting a balked or rejected landing when the aircraft bounces. Given the low-energy state of the aircraft at the time of the bounce, the first officer attempted to salvage the landing.

  4. When the thrust levers were reduced to idle after the bounce, the GLD system activated. The resultant sink rate after the GLD system deployed was beyond the certification standard for the landing gear and resulted in the landing-gear trunnion fitting failures.

  5. There was insufficient quality control at the landing gear overhaul facility, which allowed non-airworthy equipment to enter into service. The condition of the shock struts would have contributed to the bounce.

Safety action taken
On September 26, 2006, the operator sent an e-mail to all of its simulator and line training instructors to raise awareness about the dangers of landing the CRJ-series aircraft with residual thrust, reminding them that it could contribute to a bounced landing. This information was officially incorporated into the October 1, 2007, update of its line indoctrination guide, which provides guidance on administering line training.

TSB Final Report A07Q0213—Loss of Control and Collision with Terrain

On October 25, 2007, a Beechcraft A100 was conducting an instrument flight rules (IFR) flight between Val-d’Or, Que., and Chibougamau/Chapais, Que., with two pilots on board. The aircraft flew a non-precision approach on Runway 05 at the Chibougamau/Chapais Airport, followed by a go-around. On the second approach, the aircraft descended below the cloud cover to the left of the runway centreline. A right turn was made to direct the aircraft towards the runway, followed by a steep left turn to line up with the runway centreline. Following this last turn, the aircraft struck the runway at about 500 ft from the threshold. A fire broke out when the impact occurred, and the aircraft continued for almost 400 ft before stopping about 50 ft north of the runway. The first responders tried to control the fire using portable fire extinguishers but were not successful. The Chibougamau and Chapais fire departments arrived on the scene at about 09:26 Eastern Daylight Time (EDT)—approximately 26 min after the crash. The aircraft was destroyed by the fire. The two pilots suffered fatal injuries.

Findings as to causes and contributing factors

  1. The aircraft was configured late for the approach, resulting in an unstable approach condition.

  2. The pilot flying carried out a steep turn at a low altitude, thereby increasing the load factor. Consequently, the aircraft stalled at an altitude that was too low to allow the pilot to carry out a stall recovery procedure.

Image of crash site

Findings as to risk

  1. The time spent programming the GPS reduced the time available to manage the flight. Consequently, the crew did not make the required radio communications on the mandatory frequency (MF), did not activate the aircraft radio control of aerodrome lighting (ARCAL), did not make the verbal calls specified in the standard operating procedures (SOPs), and configured the aircraft for the approach and landing too late.

  2. During the second approach, the aircraft did a racetrack pattern and descended below the safe obstacle clearance altitude (OCA), thereby increasing the risk of a controlled flight into terrain (CFIT). The crew’s limited instrument flight rules (IFR) experience could have contributed to poor interpretation of the IFR procedures.

  3. Non-compliance with communications procedures in an MF area created a situation in which the pilots of both aircraft had poor knowledge of their respective positions, thereby increasing the risk of collision (see the full TSB Final Report for the analysis on this finding.)

  4. The pilot-in-command monitored approach (PICMA) procedure requires calls by the pilot not flying when the aircraft deviates from pre-established acceptable tolerances. However, no call is required to warn the pilot flying of an approaching steep bank.

  5. The transfer of controls was not carried out as required by the PICMA procedure described in the SOPs. The transfer of controls at the co-pilot’s request could have taken the pilot-in-command by surprise, leaving little time to choose the best option.

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