Scoot B789 at Taipei on Jun 19th 2023, dropped nose wheel in flight

Last Update: September 9, 2024 / 15:26:16 GMT/Zulu time

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Photo of Scoot Airlines 9V-OJF, Boeing 787-9 Dreamliner — Scoot Airlines 9V-OJF, Boeing 787-9 Dreamliner (Photo credit: BIG FOOT11 / Flickr / License: CC by-nd)

Incident Facts

Date of incident
Jun 19, 2023

Classification
Accident

Airline
Scoot Airlines

Flight number
TR-897

Departure
Seoul, South Korea

Destination
Taipei, Taiwan

Aircraft Registration
9V-OJF

Aircraft Type
Boeing 787-9 Dreamliner

ICAO Type Designator
B789

A Scoot Boeing 787-9, registration 9V-OJF performing flight TR-897 from Seoul (South Korea) to Taipei (Taiwan), landed on Taipei's runway 23L at 00:02L (16:02Z Jun 18th) and taxied to the apron seemingly without incident.

A post flight inspection revealed however that the left hand nose wheel was missing from the nose gear.

The aircraft positioned to Singapore on Jun 29th 2023 but has still not returned to service (standing Jul 3rd).

Singapore's AAIB reported tyre debris was found on a taxiway in Seoul after the aircraft had departed, after landing in Taipei the left nose wheel was missing. The aircraft sustained substantial damage. The occurrence was rated an accident and is being investigated by Singapore's AAIB.

Singapore's AAIB released their final report concluding the probable causes of the accident were:

- The aircraft’s NLG axle sheared off at the inboard journal location during taxiing in ICN to the take-off runway. The flight crew were not aware of this, and the aircraft took off to Taipei.

- Prior to landing in Taipei, the flight crew was advised by TACC of a possible tyre issue. It did not occur to them that the aircraft had only one nose wheel for the landing in Taipei.

- The aircraft manufacturer indicated that the NLG was designed with redundancy such that landing with one nose wheel could be handled just like when there was a deflated nose wheel tyre.

- While the aircraft manufacturer indicated that landing with a nose wheel missing is similar to landing with a deflated nose tyre, this piece of information is not documented anywhere for the awareness of flight crew.

- There were no injuries to the crew and passengers nor damage to properties other than the nose landing gear axle. The safety of flight was not affected due to the redundancy in design of the nose landing gear.

- There was no evidence of over-torquing of the LH nose wheel during installation.

- Results of metallurgical examinations suggest that the LH nose wheel inboard bearing had seized. This seizure resulted in the generation of high heat and eventually intergranular fracture of the LH axle. The seizure was likely due to roller skewing. However, the cause of the rollers skewing could not be determined.

- Visual bearing inspection is subjected to human factors in the inspectors’ ability to spot defects, in particular defects on the inner race surface, given the limited access. This can result in inconsistent inspection outcome.

- The investigation team could not establish the cause of corrosion found on the outboard bearing cup. However, the corrosion was not the cause of the inboard bearing failure.

The AAIB summarized the sequence of events:

On 18 June 2023 a Boeing B787-9 operated a scheduled flight from Singapore Changi Airport to Incheon International Airport (ICN), Republic of Korea via Taipei in Taiwan. After arrival at ICN, there was a change of flight crew to operate the return flight from ICN to Singapore via Taipei. The flight crew of the ICN – Taipei – Singapore sector comprised a Pilot-in-command (PIC) and a First Officer (FO). The FO was the pilot flying (PF) and the PIC the pilot monitoring (PM).

A tow tug pushed back the aircraft from parking bay 108 onto Taxiway R9. Before the tow tug turned the aircraft to align it with the centreline of Taxiway R9, the headset man of the pushback team sensed that there was some resistance during the pushback. He stopped the pushback and asked the flight crew if the parking brakes had been released. The flight crew replied that the parking brakes had been released and the headset man resumed the pushback.

When the tow tug was turning the aircraft to align it with the centreline of Taxiway R9, the flight crew felt some vibration. To the flight crew, such vibration was not unusual during ground manoeuvring of aircraft. After the aircraft was pushed back onto Taxiway R9, the tow tug was disconnected.

The FO was to taxi the aircraft to Runway 34R via Taxiways R9, R21, R10, M, M5 and S (see Figure 1). During the taxiing, vibrations were felt by the flight crew when the aircraft was turning right from Taxiway R9 to Taxiway R21 and turning left from Taxiway R21 to Taxiway R10. At about midway along Taxiway R10, the PIC took over the taxiing of the aircraft. Thereafter, no vibration was felt by the flight crew. The PIC handed the control back to the FO and the FO performed the take-off. The take-off roll, rotation, lift-off and landing gear retraction were normal.

At top of climb, the flight crew carried out an aircraft system check as required by procedure and noted a status message “tire press sys1”. On checking the wheel synoptic page on the aircraft’s Engine Indication and Crew Alerting System (EICAS) display, the crew noticed that the tyre pressure of both nose landing gear (NLG) tyres were not displayed. The flight crew discussed and noted that there were three possibilities:

(a) Faulty tyre pressure sensor
(b) Deflation of one nose wheel tyre
(c) Deflation of both nose wheel tyres

In view that the take-off and landing gear retraction were normal, the flight crew felt that it was likely an indication problem. The aircraft continued its flight to Taipei.

In the meantime, the ICN airport authority had found a nose wheel with its tyre and debris pieces along Taxiways R9, R21 and R10 and suspected that they had come from the occurrence aircraft. It reported to the air traffic control tower in ICN that a tyre was found and that the tyre was suspected to have come from the occurrence aircraft. The ICN tower reported to Incheon Area Control Centre (IACC) who in turn informed Fukuoka Area Control Centre (FACC) and FACC informed Taipei Area Control Centre (TACC) that there was a tyre issue with the occurrence aircraft.

After the aircraft had established contact with TACC, TACC informed the flight crew that the aircraft might have a tyre issue. The flight crew asked TACC for details about the tyre issue and was subsequently informed that tyre debris were found in ICN and that the debris might have come from their aircraft. In response, the flight crew informed TACC that they had lost both nose wheel tyre pressure indications. They also considered that the worst-case scenario was deflation of both nose wheel tyres. The flight crew referred to the Flight Crew Training Manual (FCTM) but there was no guidance on landing with deflation of both nose wheel tyres. Nevertheless, they noted the FCTM guidance on “Landing on a Flat Tire”4 and also considered the possibility of stopping on the runway.

The PIC took over control of the aircraft for the landing in Taoyuan International Airport in Taipei. During the approach, the flight crew took the precaution of extending the landing gears while the aircraft was over the water out of consideration that nose wheel tyre debris pieces, if any, would not fall onto populated areas. On final approach, the flight crew requested for the tower to sight the aircraft nose wheels for any anomaly. The tower replied that they were unable to do so due to limited visibility in night condition.

According to the PIC, the touchdown was normal and he did not feel any vibration during the landing roll. The PIC requested for Taipei Ground Control to sight the exterior of the aircraft for any anomaly. Taipei Ground Control advised the flight crew that they were unable to do so due to limited visibility in night condition but that an apron vehicle would be escorting the aircraft to the parking bay.

The PIC taxied the aircraft into parking bay B9 without difficulty. At the parking bay, the flight crew were informed by the ground handling staff that the left axle of the NLG had sheared off and the left nose wheel was missing.

The AAIB described the language:

The left axle of the NLG sheared off at the inboard location but the inner spacer was still in place (see Figure 2). The black charred appearance of the fractured axle face at between the 6 and 8 o’clock positions indicated exposure to extreme heat.