B733, Birmingham UK, 2012
B733, Birmingham UK, 2012
On 21 September 2012, an Aurela Boeing 737-300 lost directional control and left the paved surface when attempting to turn off the landing runway at Birmingham expeditiously to avoid the following aircraft having to go around. The Investigation noted that the range of the approaching aircraft - still 2.5nm as the incident aircraft began to clear the runway - had not been communicated and concluded that the speed of the aircraft had been inappropriate for the prevailing wet surface conditions as well as unnecessary to prevent a go around by the following aircraft.
On 21 September 2012, a Boeing 737-300 being operated by Lithuanian operator Air Aurela for Monarch Airlines on a passenger flight from Nice to Birmingham lost directional control and left the paved surface when an attempt was made to turn off wet landing runway 33 expeditiously at the end after missing an earlier exit. The excursion was minor and there were no injuries to the 143 occupants who were subsequently disembarked down external steps brought to the rear right door and transported to the terminal in buses. Damage to the aircraft was minor, being confined to the nose wheel tyres.
An Investigation was carried out by the UK AAIB assisted by Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) recordings which had both captured the event. It was concluded that the aircraft had been serviceable and so the remainder of the Investigation focused on the surface friction and the actions of the pilots as the landing roll progressed.
It was established that the aircraft commander had been PF and that the runway 33 landing had been briefed and made with autobrake 2 selected and with the plan being to vacate at taxiway ‘Bravo’ at a distance of approximately 420 metres from the end of the 2296 metre runway LDA. The aircraft landed in the TDZ at the correct speed into a slight headwind and idle reverse was then selected. It was noted that “during the landing roll the commander judged the aircraft would not decelerate sufficiently to vacate at Taxiway Bravo without excessive braking, so he disconnected the autobrake using the brake pedals just before Taxiway Bravo. He then cancelled thrust reverse, released the brakes and let the aircraft roll to the end of the runway to vacate at Taxiway Alpha.” As the aircraft approached Taxiway Alpha, the crew heard ATC transmit to the following aircraft “expect late landing clearance previous lander has gone all the way to the end” and the commander stated that he had been keen not to cause the following aircraft to go around. As the right turn was commenced the aircraft had begun to skid towards the left edge of the taxiway and with attempted braking ineffective had departed onto the adjacent grass. Having informed ATC of this, the following aircraft was instructed to go around.
It was established that no other aircraft which had landed on runway 33 that day when wet had reported any difficulties taxiing from the runway and detailed investigation of the runway and runway exit surface friction characteristics found that only a very small part of the surface used was found to be below the applicable ‘Minimum Friction Level’ for use with the available measuring equipment as described in UK CAA CAP683. The average friction level on the Alpha taxiway exit was 0.70 against the corresponding ‘Maintenance Planning Level’ of 0.63 It was therefore concluded that the available surface friction had not been a factor and specifically that it was unlikely the area of reduced friction on Taxiway Alpha had a significant effect on the (excursion) outcome “because the nose and right main gear (had only) encountered it for a maximum distance of approximately 5 metres”.
Calculations of the actual ground speed of the aircraft were made and it was found that with the aircraft at a ground speed of 36 knots, pedal braking had been applied just prior to the exit but that, when the subsequent rate of turn reached a maximum of 21 +/- 3 knots which had reduced to 14 +/- knots as the nosewheels left the paved surface. The airline Operations Manual was found to state in respect of taxi speed during turns that “when approaching a turn, speed should be slowed to an appropriate speed for conditions. On a dry surface, use approximately 10 knots for turns greater than those typically required for high speed runway turnoffs.” It was considered that “as the runway and taxiway were wet, a lower speed would have been appropriate” yet it had been commenced from above 20 knots.
The Investigation formally concluded that “the aircraft departed the paved surface of the taxiway because it turned to vacate the runway at a speed inappropriate for the conditions”.
The Final Report of the Investigation was published on 13 June 2013. No Safety Recommendations were made.