Merpati B735 at Makassar on Dec 26th 2011, temporary runway excursion on landing
Last Update: January 4, 2017 / 15:23:31 GMT/Zulu time
Indonesia's NTSC released their final report concluding the probable causes of the serious incident were:
- The reverse thrust was applied asymmetrically and no advice of the differential N1 during reverse thrust application provided
- The braking and reverse thrust application to correct the directional control was not in accordance with the published procedures.
The NTSC reported the First Officer (23, CPL, 188 hours on type) was in line training to become qualified first officer and was pilot flying for the sector. The Captain (42, ATPL, 1,339 hours total, 440 hours on type) was pilot monitoring for the sector.
The aircraft was on an ILS approach to Makassar's runway 13 when the first officer, while the aircraft descended through 550 feet, felt uncomfortable with the rain conditions and suggested to go around. The captain advised, that the runway was visible and suggested to continue the approach, took control of the aircraft and landed the aircraft about 2 minutes later, the aircraft however veered right, hit a taxi sign board, continued rolling over the runway for about 375 meters before being returned onto the runway. The aircraft subsequently taxied to the apron. There were no injuries, the right hand engine (CFM56) cowl was damaged.
The flight data recorder showed the aircraft heading at 129 degrees magnetic when descending through 20 feet AGL changing to 126 degrees at touchdown and further changing to 106 degrees during the first 8 seconds of the landing roll. The left hand thrust reverser deployed a second prior to the right hand thrust reverser, the right hand engine reached a 35% higher N1 than the left hand engine during the roll out over a period of 16 seconds. The brakes were actuated asymmetrically with more power applied on the left brakes.
The NTSC analysed:
The relative low experience of the SIC, under line training, and never having previously experienced rain condition on an approach suggested a go-around. Under these circumstances the SIC’s discomfort was understandable and the suggestion to go-around was reasonable.
The PIC’s decision to take over the control as PF was appropriate. Consequently, the directional control of the aircraft was the responsibility of the PIC as PF. The SIC advised the PF to fly left when crossing the runway threshold in order to regain runway centerline.
The FDR data recorded that at touchdown the left thrust reverser deployed a second before the right thrust reverser, momentarily resulting in asymmetric reverse thrust. Three seconds later the N1 of the right engine was greater than that of the left engine, with a momentary differential value recorded up to 35%.
The increasing of the N1 after the thrust reverser deployed would increase the drag and asymmetric reverse thrust would also createasymmetric drag. The N1 of the right engine was greater than the left engine which mean that the drag induced by the right engine was greater than the left engine. This condition led to the aircraft veered to the right.
During the landing roll, the CVR did not record any communication from the PM to the PF about the engines parameters. The SIC might not have fully adapted to the role of PM following the handover of control to the PIC. This led to the continued asymmetry of the reverse thrust, and worsening the situation.
Moreover, the FDR also showed asymmetric brake pressure application 12 seconds after touchdown, in which the average left brake pressure was 200 psi greater. The FCTM stated that the reverse thrust side force component drifts the airplane to the downwind side of the runway and high braking forces reduce the capability of the tires to corner in order to regain the aircraft direction.
The brake and reverse thrust applications were not in accordance with the FCTM procedure for regaining the directional control and consequently led to the aircraft diverging from the runway during the landing roll.
This article is published under license from Avherald.com. © of text by Avherald.com.
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