Myanmar E190 at Mandalay on May 12th 2019, nose gear failed to extend
Last Update: June 16, 2020 / 16:35:24 GMT/Zulu time
The airline reported the aircraft was on its way from Yangon to Mandalay when on approach to Mandalay the crew could not extend the nose gear. The aircraft overflew the runway twice to have tower check the landing gear. The aircraft entered a hold to burn off fuel.
On Jun 16th 2020 Myanmar's DCA released their final report concluding the probable cause of the accident was:
Maintenance actions were not properly done as per the fault isolation manual in rectifying the intermittent Weight off Wheels System Fail fault and in addition, poor workmanship in performing the Nose Landing Gear Strut N2 servicing.
The DCA reported:
The flight crew comprised of the Pilot- in-command (PIC), a safety pilot and a trainee pilot. The line trainee pilot was the pilot flying all the way to Mandalay International Airport. He made an RNP approach to runway 17 when he was 7 nm away from the runway. Twenty seconds after he commanded the landing gear control lever to DOWN, a LG LEVER DISAG warning message appeared on the Crew Alerting System (CAS), accompanied by triple aural chimes. At that time the pilot in command took the control from the line trainee pilot and the safety pilot from the jump seat took the copilot seat. At 08:26 the aircraft informed Air Traffic Control (ATC) of the nose landing gear failure and requested the ATC's permission to fly an altitude 2000 ft with heading 270. The flight crew tried to perform an abnormal landing gear extension procedure as per the Quick Reference Handbook (QRH) two times and requested the ATC to monitor the landing gears situation. It was found that the nose landing gear door was ajar and landing gears could not be down. At 08:38 the aircraft declared May Day Call (State of Emergency) to the ATC and performed Partial or Gear Up Landing Procedure. The aircraft flew away 35nm from the Mandalay International Airport with heading 320ƒAto dump the aircraft fuel. At the same time the pilot in command announced to the passengers the emergency situation and requested to follow flight attendant's instructions. At 08:52 the aircraft made a RNP approach to the runway 17 of Mandalay International Airport and requested the airport fire station to stand by to respond to the emergency situation. At 09:06 the aircraft made the emergency landing with the nose landing gear failed to extend. The aircraft came to stop 4800ft from runway 17 threshold on the runway near exit taxiway A4 with smoke coming from the cockpit. All the passengers on board disembarked from the emergency slides according to the emergency evacuation procedure with the help of airport firefighters and crew. There were no injuries and no fire broke out.
The aircraft sustained substantial damage.
The DCA analysed:
A technical log entry on 8 May 2019 indicated that there was a WOW SYS FAIL, during the pervious flight. From the technical log records, the maintenance action performed was that of cleaning the Nose Landing Gear WOW sensors, connector and targets before returning the aircraft to service. On 11 May 2019,a set of flight crew entered into the technical log records that" the Nose Wheel tension was stronger than normal". This prompted a maintenance action on 11 May 2019 to service the NLG. This incident flight was the first flight after this maintenance action.
When the investigation team arrived at the incident site, the disabled aircraft was on the runway of Mandalay international airport. The investigation team took the visual inspection of the aircraft itself and the impact marks on the runway. The nose landing gear door was found open ajar but the nose landing gear itself was misaligned and stuck in the wheel well. For the disabled aircraft removal, they discharged Nitrogen from the oleo of the nose landing gear and managed to lever it out.
When the aircraft took off for the event flight, the NLG WOffW signal
changed from ¡§WOffW=False¡¨ to ¡§WOffW=True¡¨ as soon as the aircraft lifted
off from the ground. The ¡§WOffW=True¡¨ signal indicate that the NLG was
sufficiently extended so that the NLG self-centering cam was engaged, thus
guaranteeing that the NLG was centered at the beginning of the retraction phase.
The data shows that the NLG WOffW position signal transitioned from ¡§WOffW=True¡¨ to ¡§WOffW=False¡¨ between the time when the NLG position was last recorded as DOWN & Locked and first recorded as Up & Locked. (Note that that sample rates of the recorded data do not permit conclusion to the precise timing and sequence of the events). The ¡§WOffW=False¡¨ signal indicated that the NLG was sufficiently compressed to disengage the self-centering cam, allowing the nose gear tyre to rotate freely.
Two seconds after the ¡§WOffW=False¡¨ signal was recorded, the NLG steering angle changed from approximately 1 degree to 11.7 degrees. The exact reason for why the nose gear compressed during retraction, which allowed the tires to be rotated, could not be identified as the NLG gas and oleo chambers had to be bled for the aircraft recovery, this factual information supporting this aspect of the investigation was lost.
Due to the limited opening into the NLG wheel well, the maximum nose gear tyre angle limit for the NLG to be able to enter or exit the wheel well is8 degrees in either the left or right direction. For the event flight, as this maximum nose gear tyre angle was exceeded, there would not have been enough clearance for the NLG to leave the wheel well and it remained stuck for the rest of the flight. This resulted in the failure of the NLG to extend when repeated selected by the flight crew and requiring the eventual landing to be performed, with the NLG stuck in the wheel well.
The flight data stored on the FDR included information on 23 additional flights prior to the event flight. In all these flights, the data shows that the NLG WOffW position signal transitioned from, ¡§WOffW=True¡¨ to ¡§WOffW=False¡¨ between the time when the NLG position was last recorded as DOWN & Locked and first recorded as Up & Locked. The ¡§WOffW=False¡¨ signal indicated that the NLG was sufficiently compressed to disengage the self-centering cam, allowing the nose gear tyre to rotate freely.
While all these flights were operated uneventfully, the risk of the nose gear tyre rotating beyond the limit and getting stuck in the wheel well was present. This risk due to improper servicing of the NLG to rectify the ¡§LG WOW SYS FAIL¡¨ message.
This event highlights the importance for maintenance crew to follow the maintenance and troubleshooting guidance from the aircraft manufacturer. This will allow defects to be rectified as soon as possible, to eliminate potential flight safety consequences.
VYMD 120430Z 19010G20KT 6000 FEW020 38/24 Q1006 NOSIG=
VYMD 120330Z 18010G25KT 6000 HZ FEW025 37/25 Q1007 NOSIG=
VYMD 120230Z 18010G25KT 6000 HZ FEW025 35/24 Q1007 NOSIG=
VYMD 120130Z 18010G20KT 6000 HZ FEW025 34/24 Q1007 NOSIG=
VYMD 120030Z 17010G20KT 6000 HZ FEW025 32/25 Q1006 NOSIG=
VYMD 112330Z 18009G18KT 6000 HZ FEW025 31/24 Q1005 NOSIG=
This article is published under license from Avherald.com. © of text by Avherald.com.
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