Incident Overview
On August 23, 2019, an incident occurred involving Airbus A320 aircraft registration VN-A572, operated by Jetstar Pacific Airlines (JPA). The aircraft was undergoing a scheduled C01 maintenance check (Work Package JP-A572-C01) at the VAECO (Vietnam Airlines Engineering Company) maintenance center at Noi Bai International Airport. The maintenance was performed by VAECO personnel.
Sequence of Events
On the morning of August 20, 2019, during installation of the left-hand fan cowl door on engine number 1 following AMM task 71-1310-400-801A, a maintenance technician (referred to as NVKT#1) accidentally dropped a nut at hinge position 4 into the lower engine area. NVKT#1 searched but did not find the nut and immediately reported the loss to the foreman (NVKT#2). The foreman informed the team leader (NVKT#3), who then reported to the leadership of the on-site maintenance center.
After the incident, the maintenance team stopped work related to engine 1 and conducted a first search on the ground, around the cowl, and in crevices and channels of the engine, including the VSV actuator rings and the area around the low-pressure compressor stage 2.5. An internal work card (HBMC01) was issued for "suspected nut dropped into engine" and a borescope inspection of the low-pressure compressor stage 2.5 and surrounding area was performed. No nut was found.
On August 21, 2019, the foreman notified JPA representatives (a planner and a B1 mechanic) and a C-level technician (NVKT#4) about the suspected nut in the engine. A second search was conducted using the same areas and methods as the first, with a new work card (HBMC02). A second borescope inspection (NVSDC#2) following AMM 72-00-00-200-017B also found no nut. The C-level technician then requested an additional work card (NRC 83) for borescope inspection of the low-pressure and high-pressure compressors. The foreman issued work card 83, and a B1 mechanic (NVKT#5) performed the inspection according to AMM 72-00-00-200-017B and AMM 72-00-00-200-016B. All search and borescope activities were recorded only in temporary work cards (HBMC01, HBMC02) and not in the official maintenance records.
On the afternoon of August 21, a third search was conducted by borescope technician NVSDC#3 and NVKT#5, targeting low-pressure compressor stages 2.0, 2.3, and 2.5, and high-pressure compressor stages 3 and 4, as specified in work card 83. The inspection concluded with no nut found and video recordings were made. However, the investigation team later determined that the borescope techniques used could not fully inspect all internal areas of those stages. NVKT#5 signed off work card 83 as completed.
On the morning of August 22, NVKT#4 emailed JPA the results of the searches. Based on the three searches and normal engine parameters from a ground run earlier that day, the foreman obtained approval from two maintenance center leaders to conduct a high-power engine run for post-C check testing. The run at 11:00 AM showed normal parameters with no warnings. In the afternoon, after reviewing the maintenance package and the nut search outcomes, NVKT#4 received approval from the quality assurance leadership and signed off the C01 maintenance package on the evening of August 22. However, the quality assurance leadership requested that VAECO coordinate with JPA to consult the engine manufacturer about re-inspecting the engine to confirm the absence of the nut, as any nut inside could cause damage during operation.
On the morning of August 23, the VAECO leadership ordered a halt to the aircraft's return to service until full safety assessment of the lost nut. JPA issued a work package for borescope inspection of the combustion chamber and high-pressure turbine. During the subsequent engine borescope that evening, engine damage to multiple high-pressure compressor blades was found on engine number 1. The damage exceeded the limits specified in AMM 72-00-00-200-016B, necessitating engine replacement.
Aircraft Damage
The aircraft was taken out of service for engine replacement.
Investigation Findings
The investigation by the Civil Aviation Authority of Vietnam (CAAV) focused on compliance with maintenance procedures regarding the search for the lost nut, the organization of the search, and the sign-off of maintenance when a missing nut was not found. The investigation found that:
- The technician who dropped the nut (NVKT#1) reported it promptly but did not issue a non-routine card as per SOP 6.3.4.6.
- The foreman (NVKT#2) organized searches but did not effectively assess the search methods and did not request technical assistance as per procedures when the search was unsuccessful.
- The B1 mechanic (NVKT#5) issued work instructions based on AMM tasks but the investigation determined that completing those tasks did not provide sufficient basis to confirm the absence of the nut in the engine. The search for a suspected foreign object inside the engine is a difficult task not covered by standard maintenance documentation, and maintenance personnel did not request technical support from the engineering department as required by process 6.3.4.5.