Estimated reading time 5 minutes, 27 seconds.
An AW139 helicopter experienced an uncommanded high rate of descent during a search for a recreational fishing vessel while the crew was flying with the aid of night vision goggles in bushfire-affected low visibility conditions at night.
An Australian Transport Safety Bureau (ATSB) investigation into the May 13, 2018 incident found the pilot, who was flying under night visual flight rules, lost visual cues while descending to 400 feet above ground level to confirm the potential source of a transmitting EPIRB beacon, in the vicinity of Salt Water Arm, approximately 40 km east of Darwin. The pilot’s intent was to decrease rate of descent and airspeed before activating the helicopter autopilot’s auto-hover (HOV) mode at 400 ft above ground level (AGL), however at the point of ‘HOV’ mode activation, the AW139 was descending at over 1,300 feet per minute.
The aircrew officer, who was also using night vision goggles and was monitoring the descent from the helicopter’s main cabin, alerted the pilot over the intercom of the high rate of descent, before calling “Climb! Climb! Climb!”
By this point the pilot had clear visual cues and also detected the rapid rate of closure with the ground, and instituted a recovery in accordance with drilled emergency procedures, overriding aircraft automatics and using forward cyclic and collective to reverse the rate of descent.
The aircraft descended to a height of 31 ft AGL before attaining a positive rate of climb. Occupied with flying the recovery procedure – flying solely through the outside picture and the attitude indicator – the pilot did not observe a main transmission torque limit exceedance message.
The helicopter safely recovered to Darwin, and subsequently returned to the Salt Water Arm area on a second flight to conduct a successful search for the source of the EPRIB transmission, found to be a small recreational fishing boat.
Describing the effect of smoke on pilots, ATSB director of transport safety Stuart Macleod said “During the approach to hover in a degraded visual environment, searching outside for visual cues drew the pilot’s attention away from the flight instruments. This resulted in flight instruments not being referenced when they were needed.
“With the aircrew officer in the helicopter’s main cabin, in anticipation of having to operate the winch, rather than next to the pilot in the cockpit, this negated the benefit of having a trained and competent crewmember to assist the pilot, resulting in a degraded monitoring capability in the approach to hover.”
Application of good crew resource management and practiced recovery techniques supported the crew in restoring control, Macleod noted.
“The crew’s use of standard patter and practiced drills allowed them to recover the situation and avert an accident.”