The Australian Transport Safety Bureau (ATSB) is continuing its investigation into an incident where a full inspection of a Virgin Australia ATR 72-600 may have failed to discover structural damage to the aircraft’s tailplane.
The ATSB says that the aircraft, registration VH-FVR, suffered overstress damage to its tailplane during a flight on 20 February 2014, but an overnight inspection failed to detect the damage. The aircraft then flew 13 additional sectors before pitch control anomalies were detected on 25 February, after which an inspection following a suspected bird strike discovered the structural damage.
The 20 February incident occurred as the aircraft was operating a Canberra-Sydney service.
At 1640 the aircraft was at 8,500 feet on approach to runway 16 Left when the crew noticed the airspeed rising quickly. The first officer reduced power, temporarily disconnected the autopilot, and manually raised the nose.
“The aircraft felt ‘heavy’, requiring the first officer’s two hands on the controls to move from the then -4° pitch angle (aircraft nose-up/down),” says the ATSB. “The first officer expected that the pitch correction would be sufficient to arrest the speed trend.”
The captain, concerned about an overspeed, raised the nose further. Though no verbal communication took place, the first officer was aware of the captain’s actions.
“To both crew members, what happened next was unexpected and unclear,” says the ATSB. “Suddenly, the crew felt high positive g, the controls felt different and spongy, and cockpit warnings activated. The crew then verified that the aircraft was under control at a stable attitude and speed. It was level or in a slight descent at an airspeed of about 230 kt.”
“One of the cockpit warnings was ‘pitch disconnect’, indicating the left and right elevator control systems had been decoupled. This allowed for independent movement of the elevators via the captain and first officer control columns.”
After consulting the pitch disconnect checklist, it was decided the captain would land the aircraft. Meanwhile, they were informed that a cabin attendant had injured her leg, presumably during the high g event.
An overnight inspection revealed no issues, although maintenance personnel did mount a platform behind the left wing, and examine the wing surfaces and tail by torchlight. The aircraft was cleared to return to flight the following morning.
On 25 February, after operating 13 sectors, VH-FVR was operating a Sydney-Albury service . On descent, the aircraft passed through birds and although the crew did not identify a bird strike, “the aircraft’s pitch trim system fluctuated abnormally”, says the ATSB.
“[After landing] the captain conducted a walk-around inspection with an expectation of bird damage to the left side of the aircraft,” it adds. “The only abnormality found was a deformity to a fairing at the top leading edge of the vertical stabiliser, which might have been the result of a birdstrike.”
An engineer at Albury used a scissor lift to inspect the tailplane. He confirmed the fairing was damaged, but noted “significant structural damage on top of the tailplane.”
A subsequent inspection by ATR discovered broken carbon piles, cracked joint sealant, and “deformation in around the area where the horizontal stabiliser attaches to the vertical stabiliser.”
“There was also some minor damage to the rudder. The damage was assessed as being consistent with an overstress condition. Subject to further assessment and non-destructive testing, the aircraft manufacturer recommended replacement of the horizontal stabiliser, elevators, and vertical stabiliser.”
The ATSB is continuing its investigation, focusing on several areas including the cockpit voice recorder and flight data recorder information, maintenance records, and the manufacturer’s maintenance instructions.