Created Sunday, Dec 20th 2020 17:07Z, last updated Sunday, Dec 20th 2020 17:07Z
An Iran Air Fokker 100, registration EP-CFP performing flight
IR-212 from Tehran Mehrabad to Birjan (Iran), was taxiing for departure still on the eastern apron when the nose gear folded side- and backwards causing the aircraft to come to a stop on its nose with the nose gear embedded in the right edge of the wheel bay. No injuries are being reported, the aircraft however received substantial damage.
Iran's CAO released their final report concluding the probable causes were:
The event initiated by fatigue cracking in the main fitting of Nose landing gear.
The lower section of the main fitting showed multiple crack initiation points on the fracture surface; the fractured upper spigot section of the turning tube was visible inside the main fitting. The analyses shown there were cracks in the NLG main fitting and the turning tube which propagated at the same time but independently of one another.
Prior to the initiation of MF fatigue cracks: an operation or events outside of the certification envelope of the MF must have occurred for a fatigue crack to initiate at this section.
Regarding the Turning Tube; a malformed radius originating from a repair of the turning tube led to a double radius feature, locally increasing the stress which resulted in fatigue crack initiation.
The most probable sequence of events is that the main fitting fractured first, causing the collapse of the leg. Base on SAFRAN Landing Systems report TE-GL-00159023 the fracture of main fitting (fatigue crack initiation) was occurred during the life of the component.
Contributory Factors:
Lack of preventative inspection task as Single visual inspection of AMM for rough towing to detect failure is found.
Maintenance process of nose landing gear was not effective to prevent incident.
The CAO analysed:
Aircraft has started normal taxi on the apron. Nose landing gear was broken while turning to the left. The broken nose landing gear with following specifications was dispatched to the SAFRAN landing gear system services UK LTD, for more investigation:
Part No. : 201071001, Serial Number: DRG/10655/89
NLG CSN: 42028 Cycles
NLG CSO: 1250 cycles.
Date of delivery from factory: 10th, Nov. 1989
Date of last installation: 30th, Dec. 2015
The history of first NLG overhaul showed that it was done in Fokker service on 2001 and related documents was not sent to the Iran Air, so Iran Air could not follow real safe life limits in accordance with Fokker service Airworthiness limitation section report SE-623.
There was already AD 2012–0002 R1 issued by EASA which:
- Mandated replacement of NLG with P/N; 201071001 or 201071002 units with new modified 201071003 or 201071004 NLG units. This replacement should be done no later than the next scheduled main fitting overhaul which postponed by Iran Air by misunderstanding of AD contents The NLG overhaul has been performed since issuance of mentioned EASA AD and the fractured NLG should have been replaced in accordance with the instructions within it.
- Mandated repetitive inspection as per SBF100-32-118(based on Messier-Dowty SB F100-32-92) for periodic NDT of the main fitting which was done by Iran air on 75 cycles before incident time.
- The length and cumulative striation count (4530) for the largest main fitting crack and the length and cumulative striation count (10436) for the turning tube crack are strong evidence that these fatigue cracks were present on these components during that overhaul and could not been detected during the NDT inspections .
The upper section of the nose landing gear (Photo: CAO Iran):
EP-CFP sitting on its nose (Photo: Iran Aviation):
Detail of the nose gear:
