Royal Maroc AT72 at Ben Slimane on Jul 27th 2016, rejected takeoff twice resulting in wheel fire
Last Update: March 12, 2021 / 18:57:03 GMT/Zulu time
Morocco's AIB rated the occurrence a serious incident and opened an investigation reporting, there were no injuries, the aircraft sustained minor damage.
Some time in the past (discovered only on Mar 12th 2021 following a re-design of BEA Maroc's website) the Maroc's BEA released their final report in French only (editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a French only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe.)
The report concludes the probable causes of the serious incident were:
- obstruction of pitot probes that caused an underreading of airspeeds on takeoff
- the difference in airspeeds was not identified during the first takeoff run due to failure to apply the operational procedures
- excessive actions and excessive braking following the two rejected takeoffs as well as high speed taxiing with engines in flight idle
Contributing factors were:
- lack of ATR procedures for cooling brakes after a rejected takeoff
- time pressure related to airport closure
- failure at cockpit resource management level
- human factors related to stress and strong authority gradient between captain and first officer
- risks associated with the Ben Slimane Aerodrome's environment that could clog pitot tubes without cover (presence of insects and impurities)
The BEA reported the captain (51, ATPL, 14,000 hours total, 6,500 hours on type) was pilot monitoring, the first officer (46, CPL, 4,776 hours total, 1,286 hours on type) was pilot flying.
When the aircraft attempted the first takeoff run, an airspeed problem occurred, however, the takeoff was continued, the aircraft lifted off reaching 5 feet AGL by itself undetected by the crew however could not sustain flight touching down again 17 seconds after lift off at which point the commander decided to reject takeoff. The aircraft returned to the threshold runway 32 and attempted another takeoff run 5 minutes after the first. This time the takeoff was rejected upon an "IAS DISAGREE" indication, taxied to the end of the runway, vacated the runway. While taxiing towards the apron tower advised the crew of fire at the right hand engine (PW127M) and alerted emergency services, the crew stopped the aircraft, applied the fire checklist for the right hand engine and evacuated the aircraft. Fire fighters put the fire at the landing gear out.
The BEA reported the aircraft had just come out of a an A check performed by the company's maintenance workshop located at Ben Slimane Airport.
The BEA analysed that the airline had a staffing problem. The captain of the flight arrived for the occurrence flight only one hour prior to closure of the aerodrome. In addition, the flight plan had not yet been activated at that point, so that the crew before engine start needed to call in to activate the flight, which added additional stresses to the crew. This management of flight crew as well as flight planning thus contributed to the serious incident.
The interventions by tower and emergency services of Ben Slimane were timely and effective, which prevented further damage. The BEA annotated that the tower controller had granted an additional 5 minutes past the closure time of the aerodrome when the crew conducted their second takeoff run and tower subsequently reported there was fire from the right hand engine.
A blow test on the pitot probes confirmed debris in all (!) pitot tubes. The left hand pitot tube was "slightly obstructed", the right hand pitot probe was "obstructed", the standby pitot probe was "very clogged".
The Ben Slimane Airport environment is characterised by vegetation and straws, which in the summer period become a potential danger of infiltration of small grains of straw or dust in pitot probes and static ports but also pose a high risk of insects entering these probes and ports. Protective measures like covers could have prevented the accumulation of impurities inside the pitot probes.
The high authority gradient in the cockpit with the company's air operations manager and instructor at the controls as captain in relation to the first officer might have contributed to the serious incident. The first officer stated in his post occurrence interviews, that he had high esteem for the captain and thus felt unable to speak up, also because of anxiety due to the time pressures because of the impending aerodrome closure. In addition, the commander communicated with tower in French and Arabic, both languages were not understood by the first officer.
During the first takeoff run the indicated airspeed did not exceed 70 KIAS when the takeoff was rejected about 16 seconds after full throttle was applied. During that time the calibrated airspeed had risen to 97 knots, however, the left hand IAS was 49 knots and the right hand IAS was 35 knots, the airspeed disagree indication had illuminated, all of which was missed by the flight crew.
While the aircraft was airborne during the first takeoff run, the calibrated airspeed did actually exceed Vr of 104 knots and reached 107 knots with a speed over ground of 106 knots. However, the crew observed 56 knots at the left IAS and 36 knots at the right IAS. The crew did not attempt to provide inputs to climb the aircraft. The aircraft touched down again producing a vertical load of +1.6G. Wheels #4 and #2 were subsequently exposed to heavy load, also due to high speed taxiing with the thrust levers at flight idle for about 3000 meters. The brakes blocks ran hot.
The second takeoff run reached a calibrated airspeed of 96 knots with indications of 52 KIAS left and 34 KIAS right, the airspeed disagree indication illuminated again. This time the crew noticed the indications having been aware that they had an airspeed problem.
Although the stand by pitot probe was determined very clogged, it was identified the debris did NOT obstruct the air flow, the stand by ASI thus indicated correctly.
The fire damage (Photo: BEA Maroc):
The development of the fire (Graphics: BEA Maroc):
Point 1: Vacating the runway after second rejected takeoff
Point 2: Tracks of tyre #4
Point 3: tyre #4 deflating
Point 4: tracks of tyre #2
Point 5: traces of hydraulic oil
Point 6: start of fire at wheel #4
Point 7: start of fire at wheel #2
Point 8: aircraft stopped
This article is published under license from Avherald.com. © of text by Avherald.com.
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