Perimeter SW4 at Thompson on Nov 2nd 2017, engine problem, runway excursion
Last Update: November 23, 2018 / 17:35:41 GMT/Zulu time
The Canadian TSB dispatched investigators on site and opened an investigation. The regional manager reported the aircraft went off the runway (runway excursion) and sustained damage to gear, belly and a propeller.
NAV Canada reported the runway needed to be closed due to the disabled aircraft and fuel on the runway.
On Nov 7th 2017 the TSB reported the crew advised of a low oil pressure indication on the left hand engine during the approach to Thompson, they may need to shut the engine down. The aircraft landed on Thompson's runway 24 with both engines operating, the aircraft veered to the right and went off the runway. The left main and nose gear collapsed, the propellers contacts the ground. The aircraft came to rest in the snow north of the runway. Captain and first officer were taken to a hospital with minor injuries. The aircraft sustained substantial damage to fuselage, propellers, landing gear and right hand wing. The TSB opened a Class 3 investigation into the occurrence.
On Nov 23rd 2018 the TSB released their final report concluding the probable causes of the accident were:
Findings as to causes and contributing factors
- The left engine low oil pressure indications during the previous and the occurrence flights were likely the result of a steady oil leak past the rear turbine air-oil seal assembly.
- The loss of engine oil pressure resulted in a loss of propeller control authority on landing and the upset of the aircraft.
- After consultation with maintenance, the crew considered the risks associated with landing single engine and without hydraulic pressure for the nose-wheel steering, and decided to continue the flight with both engines running, even though this was not consistent with the QRH procedures for low oil pressure indications.
- Carbon deposits that accumulated within the inside diameter of the bellows convolutions interfered with the bellows’ ability to expand and to provide a positive seal against the rotor seal.
Findings as to risk
- If Canadian Aviation Regulations (CARs) subparts 703 and 704 operators do not provide initial or recurrent crew resource management training to pilots, these pilots may not be prepared to avoid, trap, or mitigate crew errors encountered during flight.
- If operators of the SA227-AC Metro III aircraft rely solely on the emergency procedures listed in the aircraft flight manual, continued engine operation with low oil pressure may result in loss of control of the aircraft.
- If an engine is not allowed to sufficiently cool down prior to shutdown, oil that remains trapped within hot areas of the engine may heat up to a point where the oil decomposes, creating a carbon deposit.
- If flight data, voice, and video recordings are not available to an investigation, the identification and communication of safety deficiencies to advance transportation safety may be precluded.
- The investigation was unable to determine the length of cooldown periods for the occurrence aircraft. However, a random sampling of engine shutdowns for similar company aircraft showed that 50% had not completed the full 3-minute cooldown period.
- Despite having received limited crew resource management (CRM) training, the crew demonstrated many skills and a knowledge of CRM principles.
The TSB analysed the accident sequence:
While the aircraft was on final approach, the left engine rpm began to decrease and the torque began to increase. The propeller blade angle began to increase due to insufficient oil pressure to counter the propeller spring pressure and force exerted by the propeller counterweights. The continued depletion of oil and loss of oil pressure further increased the propeller blade angle, resulting in a further decrease in engine rpm and a rise in torque.
The initial touchdown was on the right main landing gear, at which point the power levers were pulled over the flight idle gate and into beta range. As the left engine rpm dropped below 97%, the underspeed fuel governor increased the fuel flow to maintain 97% engine rpm. This increased power while the left propeller blade angle was transitioning to a higher blade angle (larger bite of air) resulted in a sudden burst of thrust. The sudden increase of thrust while the aircraft was settling on the right main landing gear, aggravated by the right wing (retreating wing) and discing right propeller,24 increased the lift over the left wing. The increased lift caused the aircraft to roll to the right, resulting in the loss of control of the aircraft.
The TSB analysed with respect to the crew resource management:
The crew had been introduced to some crew resource management (CRM) principles during flight training; however, Perimeter Aviation did not provide formal CRM training to Canadian Aviation Regulations (CARs) subparts 703 and 704 pilots at the time of the occurrence, nor was there a regulatory requirement for this training. Threat error management (TEM), a component of CRM, was not discussed during flight training. Despite having received limited CRM training, the crew demonstrated many skills and a knowledge of CRM principles, such as conducting briefings, using checklists, problem solving, and using available resources including the maintenance operations control (MOC).
While this crew implemented many CRM principles, if CARs subparts 703 and 704 operators do not provide initial or recurrent CRM training to pilots, these pilots may not be prepared to avoid, trap, or mitigate crew errors encountered during flight. Transport Canada has proposed new regulations requiring CARs subpart 703 and 704 operators to provide CRM and PDM training and these regulations will become in effect in January 2019.
With respect to decision making the TSB analysed:
The crew was assigned to and accepted to fly a ferry flight from CZGI to Thompson Airport (CYTH), Manitoba, with a known hydraulic leak and previous reports of low oil pressure. The only restriction for the flight was to fly with the landing gear down unless there was an emergency. To manage the safety of the flight, the assistant chief pilot briefed the crew and provided sample emergencies and contingencies.
Fifteen minutes into the flight, the crew observed that the left engine oil pressure dropped into the yellow band, but no other abnormal engine operation parameters were observed. The crew did not know that oil was leaking from the left engine and no information was available to the crew to confirm that it was. It was understood by flight operations and maintenance personnel that an oil leak presents on the instrument panel as low oil pressure and rising oil temperature indications. The crew consulted with the MOC in flight and it was decided that if the oil pressure dropped below the yellow band and the oil temperature increased beyond the green band, then the engine was to be shut down.
Since there was a possibility of an engine shutdown, the flight crew retracted the landing gear to minimize drag in the event of a single-engine situation. Additionally, the possible loss of hydraulic pressure, due to the pre-existing leak, would result in a loss of nose wheel steering availability, and the crew decided to keep the left engine running to mitigate the risk of losing directional control on landing due to adverse yaw during a single-engine landing.
After consulting the maintenance operations control, the crew considered the risks associated with landing on a single engine and without hydraulic pressure for the nose-wheel steering, and decided to continue the flight with both engines running, even though this was not consistent with the QRH procedures for low oil pressure indications.
CYTH 030200Z 33003KT 15SM -SN BKN013 OVC033 M20/M22 A3041 RMK SC6SC2 SLP328=
CYTH 030100Z 35003KT 15SM -SN FEW013 BKN033 M19/M22 A3040 RMK SC2SC4 SLP325=
CYTH 030000Z 32005KT 15SM -SN BKN037 M18/M21 A3040 RMK SC6 SLP323=
CYTH 022300Z 33005KT 15SM -SN BKN034 M17/M21 A3039 RMK SC6 SLP320=
CYTH 022200Z 35006KT 15SM -SN BKN035 M17/M21 A3037 RMK SC6 SLP315=
CYTH 022100Z 35004KT 320V020 15SM -SN OVC035 M16/M20 A3037 RMK SC8 SLP314=
CYTH 022000Z 34005KT 15SM -SN BKN030 OVC037 M17/M21 A3037 RMK SC5SC3 SLP313=
This article is published under license from Avherald.com. © of text by Avherald.com.
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