Preliminary information from the ATSB shows that a Virgin Australia ATR-72 flew several days with undetected structural damage.
On 20 February 2014, Virgin Australia Regional Airlines was operating an ATR 72 aircraft, registered VH-FVR, on a scheduled passenger flight from Canberra to Sydney, Australia.
The first officer, who was pilto flying on the leg commenced descent with the autopilot engaged in vertical speed mode and a target airspeed of 235 kt (15 kt less than the maximum operating speed of 250 kt).
At about 8,500 ft, the crew noticed the airspeed going up quickly and the speed trend excessively high. The first officer reduced engine power and used touch control steering to temporarily disconnect the autopilot before manually raising the nose to control the speed. 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). The first officer expected that the pitch correction would be sufficient to arrest the speed trend.
The captain was unsure if the first officer’s control inputs were sufficient to avoid an overspeed so put one of his hands on the controls and disconnected the autopilot to raise the nose further. The captain believed he indicated his intention to take over control and while the first officer could not recall it being verbalised he was aware of the captain’s actions. The first officer recalled that he took his hands off the controls, releasing touch control steering in the process. Shortly after, concerned about a high nose-up attitude, the first officer put his hands back on the controls. To both crew members, what happened next was unexpected and unclear.
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.
The crew consulted the pitch disconnect checklist and worked to identify which control column was free and working normally. Although both controls were free, it was decided that the captain would be pilot flying. During this process an intermediate airspeed around 200-210 kt was selected before reducing the airspeed to below the 180 kt specified in the checklist. The crew made a PAN call and requested runway 16 Right to minimise taxi time on the ground since a cabin attendant had been injured in the event. A safe landing was made.
Engineers were able to establish that there had not been an overspeed but a vertical load factor of 3.34 g was recorded that exceeded the acceptable limit for the aircraft weight. A preliminary walk-around visual inspection did not reveal any aircraft damage. The aircraft was removed from further service that day and towed to a distant parking area to allow for the resulting maintenance inspection to be carried out. The engineer tasked with the inspection understood that one of the duty engineers had done quite a detailed walk-around of the aircraft in daylight and found no signs of defects. Later that night wing attachment fittings were checked and the upper surface of the wing, rear fuselage and tail were inspected using a torchlight.
No defects were identified from any of the inspections and the aircraft was returned to service the next day.
Subsequent to the occurrence on 20 February, the aircraft was operated on 13 sectors, the last of which was a scheduled passenger flight from Sydney to Albury, NSW on 25 February 2014. On descent into Albury the aircraft passed in close proximity to birds, which alerted the captain to the possibility of a birdstrike. There were no indications that a bird had struck the aircraft but on the ground, the aircraft’s pitch trim system fluctuated abnormally.
The captain conducted a walk-around inspection with an expectation of bird damage to the left side of the aircraft. 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. Upon closed inspection, an engineer noted that there was also significant structural damage on top of the tailplane. The aircraft was grounded.
Information from the operator suggested that the damage to the tailplane might have been a result of the occurrence involving VH-FVR on 20 February 2014.
The aircraft manufacturer inspected the aircraft and found broken carbon plies, cracked joint sealant, and deformation in and 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.