ASN Wikibase Occurrence # 265402
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| Date: | Sunday 3 January 2021 |
| Time: | |
| Type: |  Mooney M20F |
| Owner/operator: | Private |
| Registration: | C-GYGN |
| MSN: | 221353 |
| Year of manufacture: | 1976 |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | near pper Kananaskis Lake, Alberta -
 Canada
|
| Phase: | En route |
| Nature: | Private |
| Departure airport: | Airdrie Aerodrome (CEF4), Alberta |
| Nelson Airport, BC (CZNL) | |
| Investigating agency: | TSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The privately registered Mooney M20F aircraft was conducting an instrument flight rules (IFR) flight from Airdrie Aerodrome (CEF4), Alberta, to Nelson Aerodrome (CZNL), British Columbia. The pilot was alone on board. The aircraft departed at 1120 in visual meteorological conditions and initially climbed to 14 000 feet above sea level (ASL). Shortly after levelling off, air traffic control (ATC) asked the pilot if he could maintain an altitude of 15 000 feet ASL for a portion of the flight. The pilot accepted and climbed the additional 1000 feet, levelling off at 15 000 feet ASL at 1157.
The pilot then requested a minor deviation from the route of flight to avoid entering clouds. However, during this deviation, the clouds could not be avoided, and the aircraft entered instrument meteorological conditions (IMC). Shortly thereafter, the aircraft’s attitude direction indicator (ADI) displayed the “AHRS ALIGN” (attitude and heading reference system alignment) message, and indications of attitude (pitch and bank) were lost while indications of airspeed, altitude, and vertical speed were retained.
At the same time, the aircraft’s horizontal situation indicator (HSI) also indicated a failure, displaying a red X over the HDG (heading) annunciation. The pilot attempted to switch the HSI to the ADI page using the instrument’s touch screen function and selector knob, but was unsuccessful.
While the aircraft was still flying in IMC, its altitude began to fluctuate. It then began an unintentional left turn, eventually turning approximately 90° to the left of the assigned track. The pilot informed ATC of the instrument malfunction and requested to return to the Calgary, Alberta, area. At 1206, the pilot declared an emergency, reporting the loss of attitude and heading information from the aircraft’s instruments. Thirty seconds later, the pilot informed ATC that the aircraft’s HSI was functioning again. The pilot had briefly observed an image on the ADI at that time; however, the flight data recorded by the instrument indicate that AHRS data remained unavailable.
ATC provided the pilot with a heading that would turn the aircraft toward Calgary. During this turn, the pilot experienced spatial disorientation, the aircraft’s bank angle progressively increased and the aircraft began to descend. Over the next 5 minutes, control of the aircraft was lost multiple times; the aircraft entered a series of spiral dives, abrupt climbs, and at least 2 aerodynamic stalls. Flight data recovered from the ADI and HSI indicate that during these manoeuvres, the aircraft’s climb rate increased to as much as 8500 fpm, and its descent rate increased to as much as 23 000 fpm. In addition, the aircraft’s airspeed varied from a low of 43 knots indicated airspeed (KIAS) to a high of 242 KIAS, exceeding the aircraft’s never exceed speed by approximately 70 knots. The aircraft descended to as low as 8100 feet ASL (approximately 700 feet above ground level [AGL]) before abruptly climbing again.
The pilot was able to see the terrain below as the aircraft descended through approximately 8500 feet ASL and control of the aircraft was regained at approximately 8100 feet ASL. At the time, the aircraft was in the Kananaskis Valley, where nearby mountain peaks extended up to 10 364 feet ASL. Flight visibility at the time was approximately 1 statute mile (SM), and improved to 2–3 SM as the pilot descended to approximately 7500 feet ASL, while flying toward Upper Kananaskis Lake.
The pilot maintained a height ranging from approximately 700 to 1000 feet AGL and followed a road to navigate out of the Kananaskis Valley. The aircraft exited the valley at 1238, and the pilot was able to continue the flight directly back to CEF4 under visual flight rules. The aircraft landed at CEF4 at 1302 without further incident.
The investigation attempted to determine more precisely the source of the initial fault. However, no supplemental information about the instrument, possible reasons it would require realignment while the aircraft was in flight, or analysis of the occurrence aircraft’s recorded fault logs were provided to the investigation by Garmin. Therefore, the exact source of the initial fault could not be determined. Nevertheless, based on the information that was available to the investigation, it was determined that the most likely cause of the AHRS ALIGN message on the primary ADI was either an uncommanded AHRS alignment that took place during the flight or a sensor fault within the AHRS that required the instrument to be realigned once the fault was resolved.
Accident investigation:
 |
|
Sources:
TSB
Images:
Figure: TSB
Revision history:
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