The Transportation Safety Board has found that disorientation and possible lack of instrumentation contributed to the deadly plane crash on Gabriola Island in December.
“Aircraft owners must ensure that aircraft deficiencies are recorded and rectified before flight,” the TSB wrote in the safety message portion of the report in the Dec. 10, 2019, crash.
“The lack of external visual cues, the loss of instruments, and the on-set of acute stress with perceptual bias or narrowing of attention are all factors that increase the risk of spatial disorientation. In such situations, pilots may become reliant on their perceptions of motion and orientation, which would make them susceptible to disorientation.”
On Dec. 10, a Piper Aerostar PA-60-602P, a twin-engine six-seat aircraft, crashed on the north part of Gabriola Island. The three people on board – Alex Bahlsen, Allan Boudreau and Kathryn Boudreau – all died in the crash.
The Transportation Safety Board report into the crash was made public on July 27, 2020.
The TSB report, which outlines the history of the flight, states that the aircraft left Baja California Sur, Mexico on Dec. 9, for a two-day trip to Nanaimo. As planned, the plane stopped for an overnight rest at Chino Airport in California.
On Dec. 10, the plane left the Chino Airport, making a fuel stop at Bishop Airport in California. That was the last stop before the crash on the evening of Dec. 10.
Less than two minutes before the crash, as the plane was near Gabriola Island, the pilot told the control tower that he “just had a fail” and reported the plane had lost its attitude indicator.
Moments later, after the controller had not received communication from the pilot following instructions to gain altitude, the plane disappeared from radar and crashed.
“The aircraft collided with a power pole and trees in a wooded park area on Gabriola Island, BC, and then impacted the ground. The aircraft broke into pieces and caught fire,” the report says.
“As a result of being damaged in the accident, the emergency locator transmitter (Artex ME406, serial number 188-00293) did not activate.”
Possible loss of function of altitude indicator
The investigation states the aircraft was equipped with a BendixKing KI 256 flight command indicator (FCI), which is a pressure-driven attitude indicator with position sensing and digital circuitry. During the incident, the pilot told air traffic control that the indicator had failed.
The KI 256 FCI front display provides immediate visual aircraft pitch and roll attitude information to the pilot while its internal position, sensing and digital circuitry, generate a pitch and roll reference signal for use by the flight computer system (a BendixKing KFC 225), which includes the autopilot.
When the KI 256 FCI stops working, there is no indication to alert the pilot of the failure. It may become sluggish or the bars displaying the flight commands may become unstable (jittery), according to the TSB report.
The aircraft was not equipped with a second altitude indicator nor was it required to be by regulation.
The investigation determined that the FCI on board the occurrence aircraft was last overhauled in December 2015. There is no recommended overhaul interval for the KI 256 FCI.
The FCI was retrieved from the aircraft wreckage and sent for examination to the TSB Engineering Laboratory in Ottawa. Because the FCI had sustained severe structural damage as a result of the accident, the TSB Engineering Laboratory was unable to determine its serviceability.
According to the report, the investigation was unable to determine what aviation weather was reviewed by the pilot before the flight. It could also not determine who was flying the aircraft at the time of the crash. Both occupants seated in the front of the aircraft held valid pilot licences.
Aviation weather forecasts for the Nanaimo Airport available before the plane left Bishop Airport indicated light southeasterly surface winds, with light drizzle and mist.
The aerodrome routine meteorological report for the Nanaimo Airport at 6 p.m. on Dec. 10, 2019, i.e., approximately six minutes before the crash, indicated calm winds, light drizzle and mist.
According to the report, “if the autopilot disengages unexpectedly while the aircraft is in instrument meteorological conditions and one or more instruments fail, this results in a very high workload for pilots.”
“In this scenario, not only is the process of re-establishing situational awareness significantly more difficult without external visual cues, but it becomes even more difficult without sufficient internal cues,” the TSB report says.
“Pilots who are experiencing high cognitive workload conditions will be vulnerable to perceptual bias (selectively focusing attention on specific cues at the sacrifice of the wider scenario) or narrowing of attention (reducing their ability to scan and process information) through stress, and will be dependent on the remaining cockpit displays, communication with other flight crew members, and their own perceptions of motion and orientation to be able to continue the flight safely.”
The report says in addition to being vulnerable to perceptual bias or narrowing of attention, pilots who are experiencing high cognitive workload conditions—having to unexpectedly re-establish situational awareness without reference to external visual cues and with insufficient internal cues—are at an increased risk of experiencing spatial disorientation if they rely too heavily on their perceptions of motion and orientation.
Spatial disorientation is the inability of a pilot to correctly interpret aircraft attitude, altitude or airspeed in relation to the Earth or other points of reference.
“When pilots do not have reliable external or internal cues to alert them to the aircraft’s orientation, they can become susceptible to vestibular illusions,” the report says.
“These illusions can cause pilots to sense that the aircraft is level even though it is in a bank or pitched up or down. This illusion may continue unrecognized until the aircraft impacts terrain.”