Ryanair B738 at London on Sep 15th 2017, dropped nose wheel
Last Update: September 13, 2018 / 14:12:10 GMT/Zulu time
Date of incident
Sep 15, 2017
London Stansted, United Kingdom
ICAO Type Designator
The airline confirmed the aircraft dropped the left hand nose wheel after takeoff and diverted to East Midlands. The passengers disembarked normally and will be taken to Copenhagen by a replacement aircraft.
The UK AAIB have dispatched a team of investigators to East Midland and have opened an investigation into the occurrence.
A replacement Boeing 737-800 registration EI-EVW was estimated to reach Copenhagen with a delay of 4.5 hours.
On Sep 13th 2018 the AAIB released their final bulletin concluding the probable causes of the accident were:
The nosewheel was found to have separated from the aircraft because the NLG axle had failed at the left inboard journal. The failure was caused by a crack that had initiated near the 6 o’clock position of the journal and had then propagated over time via fatigue and SCC until the remaining material failed in overload. The crack was the result of heat-induced cracking and material property changes caused by abusive grinding of the chrome plate during the part’s last overhaul.
The cause of the abusive grinding could not be determined, but the abusive grinding would probably have been identified if a post-grinding Barkhausen inspection had been carried out.
The AAIB reported:
As the aircraft entered the runway, ATC cleared the crew to take off. The commander taxied the nose of the aircraft beyond the centreline to line up on the centre of the runway for a rolling takeoff. As he did so, the flight crew heard a noise similar to the nosewheels passing over a runway centre light. The same noise was heard by the two cabin crew members at the front of the cabin. Neither the pilots nor the two cabin crew members considered the noise to be anything out of the ordinary.
The commander reported that during the takeoff roll, despite there only being a light wind at the time, he used aileron and rudder to keep the aircraft straight on the centreline, as if the aircraft was experiencing a crosswind from the right. The takeoff otherwise appeared normal to the flight crew and, after rotation, the gear was raised with no apparent problems. They continued with the CLN 1E departure given by ATC, before being given a radar heading and climb to FL170.
An aircraft operating on a different radio frequency to EI-DLV and waiting at the S1 hold, informed ATC that, as EI-DLV had started its takeoff roll, they had seen one of the nosewheels depart the aircraft and be blown off the runway into the area behind the threshold. They could also see what appeared to be a part of the aircraft on the runway. ATC ordered a check of the runway and the aircraft parts were recovered.
When ATC notified EI-DLV of what had happened, the aircraft was passing about FL110. The crew entered a hold whilst they assessed the situation. The most appropriate guidance they could find in the aircraft manuals was for ‘landing with a flat tyre’ in the Flight Crew Training Manual, which they elected to follow. The crew decided their best option was to return to Stansted, a decision agreed when they contacted the company’s engineering base at the airport by radio. The flight crew informed ATC of their intention to return to Stansted and the commander gave the cabin supervisor an emergency brief before advising the passengers of the situation over the PA.
Having prepared the aircraft for the approach, the crew was cleared by ATC to descend and head towards the ABBOT holding and arrival point for Stansted. Shortly afterwards ATC contacted the crew to inform them that the aircraft operator had requested that the aircraft now divert to either East Midlands or Prestwick, rather than Stansted. As this conflicted with the request from the engineering base, on arrival at ABBOT the crew took up the hold in order to contact the company Operations Department by radio via their ground handling agent at Stansted. The Operations Department confirmed the new diversion preferences and the crew determined they had sufficient fuel to divert to East Midlands. The crew then re-briefed and set the aircraft up for a diversion to East Midlands before advising ATC of the new diversion request, at which time they also declared a PAN. The weather report for East Midlands was for light winds, good visibility and a broken cloud base of 3,700 feet aal.
ATC gave the crew vectors to establish on the ILS for Runway 27 at East Midlands Airport. When established on the approach, the crew flew a CAT 1 ILS, lowering the gear early; the gear operated normally and gave the normal indications. They elected to use full flaps (flaps 40) for landing to give a lower touchdown speed and calculated that autobrake 2 was the lowest usable autobrake selection they could use, as advised in the guidance they had consulted earlier. The commander disengaged the autopilot just below 500 feet aal and, on touchdown, lowered the nosewheel as gently as possible onto the runway. He reported the
landing appeared normal and that he stopped the aircraft on the runway. The fire service attended quickly; they inspected the aircraft and confirmed that one of the nosewheels was missing. The commander decided against taxiing the aircraft off the runway as the taxiway entrances ahead of them were all at 90° to the runway and he was concerned about putting stress on the remaining wheel. The engines were shut down and the passengers were deplaned onto buses before the aircraft was towed to a stand.
The AAIB analysed:
The NLG axle failed as a result of a crack that had initiated near the 6 o’clock position of the left inboard journal and had then propagated over time via fatigue and SCC until the remaining material failed in overload. The final failure occurred as EI-DLV turned onto the runway prior to takeoff.
The initial cracks had developed because the journal, whilst being overhauled, had experienced a re-tempering burn near the 6 o’clock position during post-chrome plate grinding. This abusive grinding would have resulted in heat-induced cracking in the base metal that probably grew by hydrogen embrittlement cracking during the cadmium plating process, prior to the stress relief bake. If the cracks had extended through the chrome surface from the base metal then they were probably microscopic cracks as they were not detected during the post-grinding visual inspection. The MPI did not detect any cracks but it will not detect cracks in non-ferrous material such as chrome, and it may not detect cracks in steel beneath a chrome layer. There was no requirement to perform an FPI which might have detected cracks in the chrome plating. Because no cracks were detected, the part was returned to service. Over time, in-service axle flexure caused fatigue cracks to initiate from the hydrogen embrittlement region, and propagate through the wall of the axle. This flexure probably also caused through thickness cracks to develop in the chrome plating, at locations coincident with the base metal cracks. These cracks would have allowed moisture to reach the advancing crack tip and cause the fracture to continue to propagate by the observed alternating modes of SCC and fatigue, until final ultimate fracture occurred by ductile separation through the remaining intact axle wall.
Aircraft Registration Data
Date of incident
Sep 15, 2017
London Stansted, United Kingdom
ICAO Type Designator
This article is published under license from Avherald.com. © of text by Avherald.com.
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