Description

On 12 September 2003, a Saab 340B being operated by UK regional airline Loganair on a scheduled passenger flight from Aberdeen to Kirkwall experienced a loss of pitch control during landing at destination and the rear fuselage contacted the runway causing damage to the airframe. Once the aircraft had cleared the runway, some passengers and some of the hold baggage was removed before the aircraft was taxied to its parking position because of a suspicion that the aircraft might have been loaded contrary to the accepted load and trim sheet.

Investigation

It was established that the First Officer had been PF and that the flight crew had detected abnormal pitch control during the approach as soon as Flaps 35° had been set with the First Officer stating that she had "run out of (nose down) trim". However, they concluded that the aircraft was still controllable and in particular noted that elevator control was still available. After establishing the aircraft on the final approach at about 700 feet aal the flight crew discussed whether to return the flap to 20° but, having satisfied themselves that the aircraft was still controllable with control authority in all axes, they decided to continue the approach to land.

The nominated Reference Speed (Vref) of 113 KIAS was achieved over the runway threshold but as the First Officer began to flare the aircraft for touch down, she reported having remarked that it “does not feel normal". Nevertheless, the touchdown was uneventful with the thrust lever movement from Flight Idle towards Ground Idle being commenced normally. However, as both power levers were retarded below Flight Idle, the aircraft nose began to rise rapidly. The stall warning activated and despite both pilots applying full nose down elevator, the nose continued to rise until the crew lost sight of the horizon. The crew considered carrying out a go-around, but with the stall warning activated and doubts about the aircraft's controllability they decided to remain on the runway. After a "few seconds" at the maximum attitude reached, the power levers were advanced to Flight Idle and the aircraft nose pitched downwards. Following this de-rotation and the selection Reverse propeller pitch, the crew were able to bring the aircraft to a halt about 350 metres from the end of the 1430 metre long runway. The aircraft came to a stop in an unusually high nose attitude and the flight crew had to confirm with ATC that the nose wheel was in contact with the ground. The aircraft commander decided to disembark some rear-seated passengers and the hold baggage before taxiing to the ramp. The passenger bags were weighed after landing and were found to be 215 kg more than shown on the load and trim sheet. A further weight and balance calculation was then made using the actual weights and distribution found and this disclosed that the aircraft had been 85 kg over maximum take-off weight, the maximum load for one of the two rear baggage compartments had been exceeded by 45 kg and the aircraft had operated with a centre of gravity (CG) position beyond the aft limit for both take off and landing.

The investigation considered that the principal event in the sequence of events leading to this accident was the mis-loading of the aircraft holds in Aberdeen, which was not in accordance with the loading instructions issued. It was also noted that “despite this operation of the aircraft with the CG position beyond the aft limit there were other factors that also contributed to the tail scrape.” It was seen from the Flight Data Recorder (FDR) data that the power levers had been prematurely moved to Flight Idle at 69 feet agl much earlier than recommended by the Company Operations Manual. The Investigation further noted that “the landing flare, which the (Operations Manual) recommends should be 'initiated when the main gear is a few feet above the runway', commenced at about 50 feet radio altitude and that, coincident with the elevator input to increase the pitch attitude for the landing flare, the pitch trim, which by this stage was not fully nose down, started to run in the nose up sense.” As a result of these factors, the aircraft eventually touched down with a pitch attitude of 8.3° compared to the 4-5° recommended and did so at an abnormally low speed of Vref - 20 knots.

The overall conclusion was therefore that the lower than normal de-rotation after touchdown had been the result of a combination of the high landing pitch attitude, the elevator position and the abnormal aft centre of gravity position. The major contributors to the nose up pitch change were the negative thrust generated at Ground Idle power in combination with the aft centre of gravity. The inability of the flight crew to lower the nose using full nose down elevator was due to a reduction in elevator effectiveness caused by a combination of low speed and a change in airflow over the elevators caused by the negative thrust produced by the Ground Idle power setting.

The Final Report of the Investigation was published on 5 August 2004 and may be seen in full at SKYbrary bookshelf: AAIB Bulletin No: 8/2004 Ref: EW/C2003/09/03

No Safety Recommendations were made.

Further Reading

• Loss of Control
• Mass and Balance
• Aircraft Load and Trim
• Loading of Aircraft Holds