Created Monday, Sep 28th 2020 15:11Z, last updated Wednesday, Mar 13th 2024 14:51Z
An Omni Air Boeing 767-300, registration N423AX performing flight OY-703 from Kabul (Afghanistan) to Bucharest Baneasa (Romania) with 49 passengers and 15 crew, landed on Baneasa Airport's runway 07 with all gear struts down at 14:53L (11:53Z) and locked but about two seconds after smooth touchdown suffered the collapse of the left main gear. The aircraft skidded along the runway on its right main gear, aft belly and left engine cowl, nose gear lifted off the ground again, to a stop on the center line of the runway. The aircraft was evacuated via slides. No injuries are being reported.
The aircraft was supposed to continue on to the USA following the stop in Bucharest to refuel.
Romania's AIAS (Civil Aviation Safety Investigation and Analysis Authority) reported the left main gear failed during roll out. AIAS have appointed an investigation commission. A preliminary report can be expected in 30 days.
The airport remained closed until Sep 3rd 2020 until the aircraft could be moved off the runway.
The Aviation Herald learned the aircraft sustained an upper strut body fracture.
On Sep 28th 2020 Romania's AIAS released their preliminary report in Romanian (the English version became available on Oct 1st 2020) reporting the crew consisted of captain (64, ATPL, 17,858 hours total, 5,463 hours on type) being pilot monitoring, a first officer (58, ATPL, 8,838 hours total, 718 hours on type) being pilot flying. An augmenting captain and first officer as well as 11 flight attendants completed the crew.
The aircraft performed an ILS approach to runway 07, all checklists were processed, the approach was stabilized, a "normal positive runway contact" (touchdown) at +1.6G occurred in the touch down zone. Shortly after touchdown the left main gear failed and the aircraft continued on the left engine. Upon failure of the left main gear the crew received an unsafe left main gear indication following by a left engine fire warning. The crew shut the left engine down and activated the fire suppression system, the fire indication ceased. After the aircraft came to a stand still, the commander ordered the evacuation of the aircraft via the right hand doors. As result of the evacuation a flight attendant suffered a minor abrasion as result of rubbing a hand with the surface of slide.
The aircraft had accumulated 71,418 flying hours in 14,811 flight cycles.
FDR und CVR have been successfully downloaded.
On Sep 2nd 2021 the AIAS released an interim notification stating the investigation is continuing. The outer cylinder of the left main gear had undergone a thorough metallographic examination at the Boeing headquarters in Seattle and stated: "Preliminary results showed that the characteristics of the breaking surface are consistent with a mechanism for initiating deterioration of the base material due to its overheating, followed by a hydrogen assisted cracking propagation mechanism. The examinations identified, in the areas adjacent to the rupture zone, numerous damages of the base metal under the chromium layer. The expertise report of the outer cylinder of the landing gear is being drafted. At present, the investigation continues with the analysis of the procedures and processing processes applied to the outer cylinder during the last overhaul of the landing gear."
On Mar 12th 2024 Romania's SIAA released their final report concluding the probable causes of the accident were:
The cause of the accident was the fracture of the outer cylinder of the LH-MLG immediately after touch-down, during the landing roll.
Contributing factors:
- The fracture of the outer cylinder of the LH MLG was the result of base metal heat damage caused by abusive grinding due to an inner diameter grinding machine that was found to be operating outside of input parameters, during the overhaul process performed in 2015.
- Not performing an NDT inspection between the chrome plating cycles during the overhaul process performed in 2015.
The SIAA analysed:
Operational Analysis
According to the data recorded by DFDR and analyzed by the investigation commission, after a flight of 05:45 hours, at 11:54 UTC, the aircraft touched down on the Rwy07, after a stabilized approach.
The runway touchdown was recorded by the main gear tilt sensors with the RH MLG, and the LH MLG making nearly simultaneous runaway contact. Sudden fluctuation in FDR recorded lateral, longitudinal and vertical accelerations indicate the left main landing gear collapsed shortly after the airplane landed and approximately 2950 feet beyond the runaway threshold.
NOTE. The breaking of the LH MLG Outer Cylinder occurred suddenly, across its cross-section from the cylinder inside diameter towards its outside diameter, at a distance of 78 to 82 cm (31-32 inches) from the bottom, as a result of the strut cylinder material failure.
After the LH MLG broke, the wheels truck reached the vertical position and the aircraft fell on the LH Engine nacelle. The aircraft rolled slightly towards the left. Sensing the evolution, the captain applied control inputs to maintain directional control.
Following LH Engine nacelle contact with the ground, probably due to heat induced by engine cowl friction with the ground, an engine fire indication occurred. The crew performed the appropriate “Engine Fire” checklist procedure and the fire indication stopped.
After reaching the final position, the nose of the aircraft raised and passengers’ evacuation was initiated on the RH side.
Maintenance Procedures Analysis
The results of the tests performed and reviewing the documentation of the last overhaul inspection revealed that the fracture of the outer cylinder was caused by damage due to overheating in the base metal due to the result of an inner diameter grinding machine that was found to be operating outside of input parameters.
The Inner Diameter (ID) of the outer cylinder surface had multiple cycles of chrome plate application and stripping, along with multiple grinding and polishing operations to that plating and the underlying base metal.
The investigation commission did not identify any NDT inspection carried out between the chrome plating cycles.
Related NOTAM:
A2956/20 NOTAMN
Q) LRBB/QMRLC/IV/NBO/A /000/999/4430N02606E005
A) LRBS B) 2008281300 C) 2008291300
E) RWY 07/25 CLSD.
