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CRJ9, Entebbe Uganda, 2018
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|On 4 February 2018, a Bombardier CRJ900 which had just arrived at Kigali after a flight from Entebbe was found to have identical damage to all left engine fan blade trailing edges and a small bolt was subsequently found trapped in the intake acoustic lining. The Investigation concluded that the recovered bolt had probably been picked up by the outboard left main gear tyre at slow speed and then ejected into the engine as wheel speed increased during takeoff thus causing the observed damage. FOD mitigation measures at Entebbe, where a major airside construction project was in progress, were faulted.|
|Actual or Potential
|Ground Operations, Loss of Control|
|Aircraft||BOMBARDIER Regional Jet CRJ-900|
|Type of Flight||Public Transport (Passenger)|
|Origin||Entebbe International Airport|
|Take off Commenced||Yes|
|Flight Phase||Take Off|
|Location - Airport|
|Airport||Entebbe International Airport|
|Tag(s)||Inadequate Airport Procedures|
|Tag(s)||Maintenance work in progress|
|Damage or injury||Yes|
|Causal Factor Group(s)|
On 4 February 2018, a GE CF34-8C5 powered Bombardier CRJ900 (9XR-WH) being operated by RwandAir on a scheduled international passenger flight from Nairobi to Kigali via Entebbe as WB465 completed an apparently normal flight in daylight VMC. However, a routine external inspection after engine shutdown at Kigali found that all 28 fan blades on the left-hand engine were similarly damaged at the outermost parts of their trailing edges. The aircraft was withdrawn from service for an engine and nacelle change.
A Serious Incident Investigation was carried out by the Aviation Accident Investigation Division (AAID) of the Rwanda Ministry of Infrastructure in accordance with the principles of ICAO Annex 13.
It was established that the flight into Kigali was the fourth sector of a return flight from Kigali to Nairobi via Entebbe in both directions with the same flight crew accompanied by an aircraft maintenance technician as a crew member. External checks of the aircraft with no findings were performed prior to the departures from Nairobi and Entebbe and again after arrival back at Kigali. These Checks were performed at night in Nairobi and thereafter in daylight. During landing on the 3279 metre-long runway 28 at Kigali, it was noted that, as recommended in applicable operational procedures, idle reverse was likely to have been selected thus no significant reverse thrust would have been used. It was also noted that between a runway inspection carried out at Kigali which had recorded nothing abnormal and the landing of the Entebbe flight approximately an hour later, there had been two takeoffs and one other landing on the same runway with no FOD reports. There were also no abnormal findings from the next runway inspection after the landing.
Following the initial post-flight finding of damage to all left-hand engine fan blades, further investigation led to the discovery of a metal bolt “stuck in the acoustic lining of the upper part of the fan intake” (see below). Subsequent examination of the engine at the overhaul facility found that there was no damage to the engine other than that first seen to the fan section upon visual inspection.
Photos of the recovered bolt were sent to Boeing and then to the National Transportation Safety Board (USA) (NTSB) who “concluded unambiguously that the bolt did not originate from the engine itself” and further observed that all the damaged fan blades “look like they experienced hard impact damage, consistent with impact from the bolt that was found lodged in the inlet”. As to the potential non-engine origin of the bolt, the NTSB noted that it would be very hard to determine this since “it could have come from a number of non-aviation sources (such as) fuel trucks, baggage carts and air stairs”.
It was noted that the same post flight inspection which had found the fan blade damage also found previously undetected damage to the left main landing gear outboard tyre in the form of a single “punch-type” tread depression (see the illustration below).
It was considered that direct ingestion of a bolt such as the one recovered from the engine was unlikely given the relatively high position of the tail-mounted engines but that this tail-mounted position meant that a small object released from a main gear wheel rotating at high speed was capable of being directed towards the engine inlet.
Overall, it was considered that although it “could not be demonstrated unambiguously due to lack of available data”, the available evidence all indicated that the most likely scenario was that either during taxi-out or on the runway at a low speed at Entebbe, the bolt was picked up by the left-hand outboard tyre and then came loose from it due to centrifugal force as the wheel speed increased and was ingested by the left-hand engine whilst it was running at a high rotational speed.
The Investigation noted that on the day of the event, a large airside construction project was in progress involving the extension and strengthening of both the main (17-35) and secondary (12/30) runways and their associated taxiways F, G and H. However, despite making several requests, the Investigation had not been provided with any information on the Entebbe Airport Authority’s FOD prevention programme and runway inspection regime. A similar request made to the Kigali Airport Authorities was noted to have yielded only two handwritten runway inspection sheets which indicated that “some 20 runway inspections per day were carried out in an irregular pattern”.
Current guidance on the inspection of manoeuvring area surfaces aimed at addressing the risk of FOD including that contained in ICAO Doc 9137 Part 8 Airport Operational Services (First Edition 1983) and the 4th Edition (2010) of the ACI Airside Safety Handbook was reviewed and forthcoming updates to ICAO guidance and to intended EASA Regulatory action relevant to the FOD risk were also noted.
It was considered on the basis of any evidence to the contrary that both Entebbe and Kigali airports “should make an effort to develop and implement both a comprehensive FOD prevention programme and criteria for their runway inspection regime” with such a programme and criteria being “clearly documented in their respective Airport Operations Manuals”. In addition, it was particularly considered that the fact that the extensive airside works at Entebbe were likely to continue for “years to come” meant that an early evaluation of the opportunities to mitigate the construction FOD risk there was essential.
Four Safety Recommendations were made as a result of the Investigation as follows:
- that the Kigali and Entebbe Airport Authorities develop, document and implement policies and procedures for Foreign Object Debris (FOD) prevention.
- that the Kigali and Entebbe Airport Authorities develop, document and implement policies and procedures for runway inspections.
- that the Kigali and Entebbe Airport Authorities, when establishing their FOD prevention programme, to take into account the proactive FOD prevention guidelines as proposed in EASA amendment 2018-14 that will be adopted by ICAO by the end of 2020.
- that the Entebbe Airport Authorities, in view of the continuing extensive works on the manoeuvring area, evaluate and intensify where needed their efforts to control FOD, both proactively and reactively, without delay.
The Final Report of the Investigation was published on 29 July 2019 and subsequently made available online.
- Foreign Object Debris (FOD)
- Foreign Object Debris and Damage Prevention
- Flight Crew Pre Flight External Check
- Airside Safety Handbook 4th ed., ACI, 2010