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3rd of December 2019, Stall without warning, Blog #628

A British Aerospace Bae-125-800A had to be repositioned from Detroit-Willow Run Airport to Detroit-Coleman A. Young International Airport (Michigan, USA) on this day in aviation history, the third of December 2019. Onboard the aircraft for the short ferry flight were the pilot in command (as Pilot Flying – PF) and a co-pilot (as Pilot Monitoring).

The aircraft in its final position, note the twisted/bent right-hand wing. (Source © Unknown)

After an uneventful take-off and short flight, the crew was cleared for an ILS approach to runway 33 at Coleman A. Young Municipal Airport. The weather at the time was reported as;

- Wind - 280◦C at 8 knots

- Temperature - -2◦C

- Dewpoint - -3◦C

- Clouds - overcast at 1000 ft AGL (Above Ground Level)

- Altimeter - 29.86 inHg (1011 hPa)

Other crews had reported icing between 1,600 ft and 4,000 ft. Most reports indicated light rime-type icing being encountered with moderate rime to mixed icing encountering the second highest number of reports. While on the approach the aircraft broke out of the clouds at approximately 1500 ft AGL, unbeknown to the crew the aircraft had picked up some rime ice during the descent through the clouds. Based on reports from other pilots ATC informed the crew about the possibility of ice built up. The crew reacted to this information by turning on the TKS [Tecalemit-Kilfrost-Sheepbridge Stokes] weeping wing deicing system. (A TKS system utilises a de-icing fluid that was made to seep through a porous strip along the wing and tail surface leading edges where it would then be spread out by the airflow. Anti-icing fluid for the system is stored in a tank with a total capacity of 5.55 US gallons, which provides priming and protection for about 61 minutes).

For reference, a generic Tecalemit-Kilfrost-Sheepbridge Stokes] weeping deicing system. (Source; Public Domain © Unknown)

As the aircraft continued its approach all looked normal until, suddenly without warning, the right wing and an aerodynamic stall occurred. The aircraft touched down on runway 33, went off the runway, travelled through a grass field, and crossed a taxiway, before coming to a stop near the control tower. The PF stated that there had been no stall warning (stick shaker) activation during the flight.

Both crewmembers remained uninjured, the aircraft was written off as damaged beyond repair. Shortly after the accident, the aircraft was examined by Federal Aviation Administration (FAA) inspectors. Their findings were reported to the National Transportation Safety Board (NTSB) which launched an investigation into the accident. The inspectors found ice on the leading edge of one of the wings, with ice on the ground under the other wing. The outboard section of the right wing was bent upwards. The Digital Electronic Engine Controller for each engine was shipped to the engine manufacturer for fault analysis. A review of the stored data revealed that both engines were rotating, operating, and responding to power lever inputs throughout the approach and landing.

The CVR was removed from the aircraft and shipped to the NTSB for analysis, A CVR Factual Report was produced. This report confirmed the facts of the accident pilots’ statements, that the stall warning system had not been activated.

The aircraft in its final position, immediately after coming to a stop with firefighters in attendance. (Source © Unknown)

The NTSB concluded that the probable cause(s) of this accident to be:

The pilots’ failure to increase approach speed as recommended for flight in icing conditions, resulting in an aerodynamic stall and subsequent impact with terrain. Contributing to the accident was the failure of the stall warning system to advise the crew of the approaching stall.

The NTSB report, which served as the source for this blog, can be accessed by clicking on the .pdf file below;

03Dec2019 BAe125 Stall No Warning
Download PDF • 813KB

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