Winnipeg, Manitoba, 1 November 2022 — In its investigation report (A20C0107) released today, the Transportation Safety Board of Canada (TSB) identified multiple contributing factors leading to a 2020 runway excursion in Naujaat, Nunavut.
On 26 November 2020, a Calm Air International LP Avions de Transport Régional ATR 42-300 aircraft was conducting a flight from Rankin Inlet, Nunavut, to Naujaat, Nunavut, with three crew members on board. While on descent to Naujaat Airport, the crew observed abnormally low propeller rpm indications on the left engine. Shortly after touchdown, directional control was lost and the aircraft experienced a runway side excursion on the east side of the runway. The aircraft came to rest approximately 108 feet from the runway edge and sustained substantial damage. The captain received serious injuries.
The investigation determined that a contaminant inside the left propeller’s high-pressure pump caused its pressure relief valve to fail. As a result, the propeller entered a pitch-lock condition, which locks the blade pitch and prevents reverse thrust from activating. The propeller remained in that condition until the aircraft landed. The investigation also determined that because there is no indication in the cockpit of a pitch-lock condition in flight, the flight crew were not aware that the propeller had entered a pitch-lock condition. Immediately on touchdown, reverse thrust was selected by the pilot flying, resulting in the aircraft entering an asymmetric thrust state. Due to the asymmetric thrust, directional control of the aircraft could not be maintained, and the aircraft exited the landing surface of the runway.
Following the occurrence, the operator issued a Flight Operations Bulletin, which describes the condition known as pitch lock, possible causes for this condition, how to identify it, and the actions to be taken if this condition is suspected.
For more information, see the investigation page.
The TSB is an independent agency that investigates air, marine, pipeline, and rail transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
Air transportation safety investigation report A20C0107
Runway excursion
Calm Air International LP
Avions de Transport Régional ATR 42-300, C-FAFS
Naujaat Airport, Nunavut
26 November 2020
Summary
On 26 November 2020, the Calm Air International LP Avions de Transport Régional ATR 42-300 aircraft (registration C-FAFS, serial number 298) was conducting flight CAV464 under instrument flight rules from Rankin Inlet, Nunavut, to Naujaat, Nunavut, with 3 crew members on board. While on descent, the crew observed abnormally low propeller rpm indications on the left engine. At 1326 Central Standard Time, shortly after touchdown on Runway 34 at Naujaat Airport, directional control was lost and the aircraft experienced a runway side excursion on the east side of the runway. The aircraft came to rest approximately 108 feet from the runway edge. The captain received serious injuries. The aircraft sustained substantial damage.
1.0 Factual information
1.1 History of the flight
On 26 November 2020, the flight crew reported for duty at Rankin Inlet Airport (CYRT), Nunavut, at 0745.Footnote1 Before departing on the occurrence flight, they conducted a cargo flight to Baker Lake Airport (CYBK), Nunavut, in another Avions de Transport Régional (ATR) 42 aircraft and returned to CYRT.
When the flight crew boarded the ATR 42-300 aircraft (registration C-FAFS, serial number 298) to conduct the occurrence flight, Calm Air International LP (Calm Air) flight CAV464, they noted, as part of their initial interior aircraft checks, that the left and right propeller feather solenoid circuit breakers were out and not collared.Footnote2 They called the maintenance supervisor, who informed them that the breakers had been pulled as part of a routine maintenance taskFootnote3 that had been carried out the night before. At the request of the maintenance supervisor, the flight crew then reset the breakers as instructed.
At 1217, the occurrence aircraft departed CYRT destined for Naujaat Airport (CYUT), Nunavut. On board were 2 pilotsFootnote4 and a flight attendant, as well as 3539 pounds of cargo. For this instrument flight rules (IFR) flight, 1272 L of Jet A fuel had been uploaded for a total fuel load of 5150 pounds. The departure, climb-out, and cruise portions of the flight were uneventful.
At approximately 1321, while the aircraft was on descent into CYUT, the flight crew observed that the left propeller was operating at a lower rpm than normal,Footnote5 while engine parameters remained normal. They briefly discussed the situation and made various attempts to troubleshoot and identify the problem, but did not consult the Quick Reference Handbook (QRH). They were unable to identify a specific malfunction and did not take any further action.
The captain considered his options: returning to CYRT, shutting down the left engine, or both. However, there was a crosswind at CYRT and he did not want to land on a runway with compacted snow in a crosswind or initiate a long return flight to CYRT in arctic conditions, particularly with only 1 engine operating. The captain believed that the propeller indications were related to the maintenance task that had been performed prior to the flight and did not discuss the options with the first officer. The flight crew continued the approach and monitored the situation.
During the approach, the captain advanced the condition leversFootnote6 to see if he could achieve 100% propeller rpm. This was successful at first, but as engine torque was reduced on descent, the left propeller rpm started to decay. On short final, the left propeller rpm continued to decrease, and the aircraft was becoming noticeably more difficult to control.
During the landing on Runway 34 at CYUT, the aircraft initially touched down 750 feet past the threshold and the pilot flying immediately selected reverse thrust on both power levers; however, only the right propeller went into reverse. Almost simultaneously with the selection of reverse thrust, only the “LO PITCH” light for the No. 2 engine illuminated, which went unnoticed by the flight crew.
At 1326, shortly after touchdown, the aircraft swerved to the right. In an effort to prevent a loss of control, the captain attempted to use asymmetric thrust and nose wheel steering. Although directional control was maintained momentarily for approximately 40 feet, lateral control was lost and the aircraft exited the right side of the runway in a north-easterly direction.
The aircraft travelled about 500 feet through the snow adjacent to the runway before coming to rest. At some point during the runway excursion, the captain’s safety belt released, and his head struck the forward cockpit area. The aircraft came to a stop approximately 108 feet from the edge of the runway, at which time the flight crew shut down the engines with the fire handles because the condition levers were jammed.
The captain received serious injuries and the 2 other crew members received minor injuries. The aircraft was substantially damaged (Figure 1). The emergency locator transmitter did not activate.