7th of September 2023, BETA Mode, Blog #753
With a crew of two and seven passengers on board, a Fairchild SA227-DC Metro 23 (Metro 23) was operating a flight from Toronto/Lester B. Pearson International Airport (CYYZ) to Detour Lake Aerodrome (CDT9), with a scheduled stop at North Bay Airport (CYYB) en route.
After an uneventful flight from Toronto, the aircraft arrived at North Bay Airport at 08.00 LT (local time). Another passenger boarded the aircraft, and the crew prepared for the next leg to Detour Lake Aerodrome. Before departure, the first officer provided the safety briefing.
The first officer was the pilot monitoring (PM) and occupied the right seat. The Captain was the pilot flying (PF) in the left seat. The aircraft was not equipped with automation features such as an autopilot or en route vertical navigation (VNAV). The flight crew therefore flew the aircraft manually.
At 08.20 LT, the aircraft departed North Bay and was cleared direct to its destination.
When the aircraft was approximately 46 nautical miles from Detour Lake Aerodrome and descending through 16,000 feet ASL (above sea level), the cabin pressurization differential gauge indicated a loss of pressurization, and the CABIN ALTITUDE annunciator illuminated.
The passengers noticed the change in pressurization in their ears. Those seated near the rear of the cabin also heard a squealing noise coming from the rear of the aircraft.
The flight crew initiated an emergency descent and donned their oxygen masks. After levelling off at approximately 8,900 feet ASL, the crew removed their masks and began preparations to divert.
The crew followed the relevant emergency checklist and placed the cabin pressurization controller in manual mode. Following this action, the pressurization began to return to normal, with the cabin differential increasing and the cabin altitude decreasing. The remaining items on the two checklists were not completed after this point.
With the pressurization under control, the crew decided not to divert and continued towards their original destination, Detour Lake Aerodrome.
Weather information for the destination indicated winds from the north (360°) at 15 knots, gusting to 20 knots. Based on the 100° crosswind and the aircraft's direction of travel, the captain, who was the pilot flying (PF), briefed the area navigation approach using the global navigation satellite system (RNAV [GNSS]) Y approach to Runway 10 via the DUGRO transition. The planned level of service was localizer performance with vertical guidance (LPV).
The approach consisted of three segments with a 3.6° glide path, which was included in the captain's briefing. After the approach briefing had been completed, the first officer noticed that the ground speed was low and realized that the flaps had remained in the quarter position following the emergency descent. The flaps were then fully retracted.
Once the crew established visual contact with the runway, they realized that the aircraft was not aligned with the runway centreline. A go-around was called, and the captain executed it according to the published procedure.
At 10.04 LT, while the aircraft was on the final segment of the second approach, the rate of descent varied between 1,000 and 2,000 fpm. At the same time, a ground proximity warning system (GPWS) “sink rate” aural alert sounded. In response, the PF reduced the aircraft's rate of descent.
The flight crew had briefed the approach speed, which was based on the aircraft's landing weight. The planned approach speed was 140 knots indicated airspeed (KIAS), which would gradually be reduced to 115 KIAS to achieve the required landing reference speed (Vref) for touchdown.
At 10.05 LT, the captain called for the flaps to be set to full. The aircraft was then approximately 0.75 NM from the runway.
At 10.05 LT, when the aircraft was at 98 feet above the runway, the flight data recorder (FDR) recorded a negative torque value, indicating that the engines were in reverse thrust. The first officer informed the captain that BETA had been selected. The captain acknowledged this, and one second later a positive torque value was recorded. A second negative torque value was recorded on both the right and left engines just before touchdown.
When the aircraft was at 11 feet above the runway, its roll angle was recorded as 15.4° to the right, and the aircraft was in a nose-down attitude. As a result, the right wing struck the runway, causing the nose gear and right main landing gear to collapse.
The right propeller was the first to contact the runway surface, approximately 305 m (1,000 feet) past the runway threshold. The aircraft veered to the right, left the runway laterally, and slid down an embankment.
The left main landing gear subsequently collapsed, and the aircraft came to rest in an upright position approximately 47 m (154 feet) from the runway. It was facing south-southwest on a heading of 210°M.
While the flight crew was conducting the emergency shutdown, the passengers, of their own volition, began evacuating the aircraft through the main cabin door and the over-wing exits. The engines were still operating at the time.
When the first officer opened the main cabin door and realized that the engines were still running, he returned to the cockpit and pulled the engine start/stop buttons to shut them down. Both flight crew members then left the aircraft.
The aircraft was substantially damaged. Three passengers and one flight crew member sustained minor injuries.
Investigation
The accident was reported to and investigated by the Transportation Safety Board of Canada (TSB). In its report, the TSB identified the following factors as having caused or contributed to the occurrence:
The proximity to the intended destination and the high workload experienced by the flight crew resulted in a narrowing of attention. When combined with various operational pressures, this influenced the flight crew's decision to continue the second approach and attempt to land.
The captain developed a strong expectancy for aggressive braking action based on his gravel runway training and the aircraft's speed. When this expectancy was combined with the captain's high workload and the reflexive nature of initiating BETA mode, he inadvertently engaged BETA mode before the aircraft had touched down. This resulted in a loss of control and the aircraft impacting the runway.
The TSB also identified several findings as to risk, together with safety actions taken by the operator. These can be found in the TSB report, which served as the source for this blog.
The report can be accessed by clicking on the .pdf file below.
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