Created Wednesday, Nov 18th 2020 15:33Z, last updated Wednesday, Nov 18th 2020 15:33Z
A Peruvian Airlines Boeing 737-300, registration OB-2089-P performing flight
P9-127 from Tarapoto to Lima (Peru) with 147 passengers and 5 crew, had levelled off at cruise level 330 about 100nm from the airport when the captain noticed the left hand engine (CFM56) exceeded the permitted exhaust gas temperature (EGT) at 1191 degrees C, the overtemperature warning light activated. The crew performed the relevant checklists and shut the engine down. The crew declared emergency and returned to Tarapoto for a safe landing.
Peru's Comision de Investigacion de Accidentes de Aviacion (CIAA) released their final report in Spanish only (Editorial note: to serve the purpose of global prevention of the repeat of causes leading to an occurrence an additional timely release of all occurrence reports in the only world spanning aviation language English would be necessary, a Spanish only release does not achieve this purpose as set by ICAO annex 13 and just forces many aviators to waste much more time and effort each in trying to understand the circumstances leading to the occurrence. Aviators operating internationally are required to read/speak English besides their local language, investigators need to be able to read/write/speak English to communicate with their counterparts all around the globe).
The report concludes the probable causes of the serious incident were:
Poorly applied maintenance procedures that caused the re-occurrence of an erroneous EGT high temperature indication in cruise flight prompting the crew to shut the engine down and declare emergency.
Contributing factors were:
- Inadequate Quality Control, Inspection and Maintenance procedures during corrective actions prior, during and after the occurrence, which caused analysis and decisions troubleshooting the specific indications, which however were unsuitable to address the fault that had been reported by crews on a regular basis
- Inadequate instructions to staff involved in the implementation of corrective measures
The CIAA analysed, the captain as well as the first officer demonstrated full knowledge and understanding of the indications and checklist procedures, when the EGT of the left hand engine rose to 1191 degrees C. The performance of the crew was satisfactory until and including the landing.
On Jan 15th 2018 the crews had reported excess temperature, extreme fluctuations and absence of indication developed in flight. In response maintenance worked on the EGT connector, performed engine runs with satisfactory results and returned the aircraft to service. During the occurrence flight of Jan 19th 2018 the crew reported the EGT reached the maximum of 1290 degrees C and the left hand engine had vibrations. In response maintenance replaced the EGT interface terminal, performed engine runs with satisfactory results and returned the aircraft to service. During the 4th flight of Jan 20th 2018 the EGT indication went to maximum, then dropped off to 0. In response maintenance performed the cleaning of two connectors and performed engine test runs with satisfactory results. This last maintenance action definitely cleared the fault.
The analysis specifically mentioned that at no time the resistance (and insulation) between two threaded pins of the EGT terminal as well as against insulation was measured, and no manual required that check.
The interface terminal had been correctly replaced when a pin measured at 0.6MOhm towards insulation, afterwards the resistance measured above 15MOhm. The fault repeated on Jan 20th 2018 showing the problem had not been fixed.
The terminal and connectors of the EGT cable (Graphics: CIAA):
