What happened
On May 5, 2018, a Boeing 737-48EHGW, registration OB-2079-P, operated by Peruvian Air Line S.A.C., was performing a scheduled flight from Lima to Arequipa. While cruising at 35,000 feet, the flight crew observed erratic movements of the number one engine's thrust lever and fluctuating engine parameters, including N1, N2, EGT, and fuel flow. Shortly after these fluctuations began, the number one engine suffered an uncommanded in-flight shutdown.
The crew declared an emergency and initially intended to divert to Pisco. However, due to deteriorating weather conditions at the primary alternate, they diverted to Trujillo. During the descent, the crew successfully executed engine failure and in-flight start procedures, successfully restarting the number one engine at 24,000 feet. The aircraft landed safely in Trujillo with both engines operating normally.
The investigation
The investigation conducted by the CIAA focused on the mechanical cause of the engine shutdown and the maintenance history of the engine's fuel control system. Investigators examined the Main Engine Control (MEC) unit and the physical connection between the start lever and the fuel shutoff lever.
Technical analysis revealed that the cable connecting the start lever to the MEC fuel shutoff lever was not adjusted within the tolerances specified in the Boeing Aircraft Maintenance Manual (AMM). Furthermore, while maintenance personnel eventually repositioned the cable to meet required tolerances, the aircraft's logs failed to record the specific measurements taken before and after the adjustment, nor did they document the calibration status of the tools used during the process.
Findings
- The primary cause of the engine shutdown was the improper regulation of the start lever cable connecting to the MEC fuel shutoff lever, which left the component outside of Boeing-mandated tolerances.
- Inadequate maintenance and quality control processes were present during the installation of the MEC unit.
- There was insufficient technical instruction provided to the maintenance personnel involved in the installation of the MEC.
- Maintenance records lacked necessary detail regarding the specific measurements and tool calibration used during the corrective adjustment of the cable.