What happened
On 25 September 2001, an Embraer EMB-145EP, registration G-RJXG, was conducting a scheduled public transport flight from Aberdeen to Manchester. While the aircraft was on approach to Manchester International Airport at approximately 7,000 feet, the crew encountered weather activity. Although the commander had been maneuvering the aircraft to avoid cumulonimbus clouds, a lightning strike occurred as the aircraft entered a cloud.
Shortly after the strike, the first officer noted a temperature over-indication on the left engine. Within seconds, engine parameters began to decline rapidly. The crew initiated distress calls and followed established checklists for engine failure and single-engine approach. Despite the engine issues, the aircraft completed an unevently single-engine landing at 1415 hrs. There were no fatalities and no injuries among the 17 passengers and 4 crew members on board.
The investigation
An investigation by the AAIB examined the aircraft's flight data recorder and physical damage. The strike caused visible damage to the fuselage, including rivet burns and skin marks, as well as damage to the right wingtip fairing.
Analysis of the engine control units, known as Full Authority Digital Engine Control (FADEC) units, showed that the left engine experienced a significant rise in inter-turbine temperature (ITT) and a drop in spool speeds. The investigation focused on whether the lightning strike caused an aero-thermal disturbance in the engine intake. Data from lightning location systems confirmed a relatively low-power cloud-to-ground strike in the vicinity of the aircraft at the time of the incident.
Findings
- The primary cause of the engine instability was the aero-thermal effects of the lightning strike, which disrupted the airflow into the engine intake.
- This disruption initiated a compressor stall, leading to a rapid decay in engine speeds.
- The FADEC logic, designed to protect the engine from overheating, commanded an automatic shutdown once the ITT reached its maximum permitted limit.
- The engine's control software at the time lacked specific surge recovery logic to re-establish stable running conditions after such a disturbance.
- While the physical damage to the airframe was not hazardous, the event highlighted a potential vulnerability in narrow-body aircraft with side-mounted engines to simultaneous intake disruptions.