An RCAF accident report says the pilots of a CH-148 Cyclone helicopter didn’t know the aircraft would fight back when they briefly overrode the flight director on a training flight over the Mediterranean on April 29, 2020. The big helicopter rejected the control inputs from the flight deck, after the pilot initiated an agressive 180-degree turn, and dove the aircraft into the ocean at high speed, killing all six people onboard. The Canadian Press obtained an RCAF board of inquiry report that said the accident occurred when the pilot kicked the aircraft into the helicopter version of a half Cuban 8, overruling the flight director for about 20 seconds. What he didn’t know is that the flight director was programmed to try to regain control after anything more than a “momentary” pilot-induced flight director disconnect and that longer deviations from that norm were not tested. “The automation principles and philosophy that governed the Cyclone’s design never intended for the [autopilot] to be overridden for extended periods of time, and therefore this was never tested,” CP reported the report as saying.
The disconnect button for the flight director is on the cyclic and is routinely used when pilots want to assume control for a change in the flight profile. But the crew was simulating an operational requirement to hoist personnel from the deck of the HMCS Fredericton and the pilot flying abruptly pitched up and swung the helicopter into a “return to target” manoeuvre, which is similar to a half Cuban 8 used by aerobatic pilots to turn around quickly. In a helicopter it involves pitching the aircraft up and rolling inverted to reverse direction. “The report indicated the crash might have been averted if the pilot had manually chosen to turn off the autopilot during the turn,” CP reported. “But it also stated that it wasn’t unusual for pilots to override the autopilot and there were no explicit instructions in the manuals on the necessity to manually turn off the flight director.”
A second report by the military’s Directorate of Flight Safety says Sikorsky needs to address what the directorate considers to be a software issue with the “bias accumulation” function in the flight director that tracks a pilot’s manual inputs that are in conflict with the set flight profile. “We need to look at that software and see if we can eliminate this from the software altogether, being careful to understand when you make any changes like that you may introduce a butterfly effect and cause problems elsewhere,” CP quoted an unnamed source as saying.