What happened
On 14 September 2021, a Saab 340B, registration G-NFLB, was conducting a training flight near the Isle of Islay. The flight was part of a crew conversion programme, and the crew had intentionally shut down the left engine to demonstrate single-engine handling characteristics.
During the attempt to restart the left engine, the crew encountered a failure in the right engine's starter/generator. This failure caused the electronic flight instrument system (EFIS) screens to go blank, leaving the aircraft operating on battery power only. With the loss of the Flight Management Computer and several other systems, the crew faced a critical time limit before the batteries were exhausted.
To manage the emergency, the crew performed load shedding of non-essential electrical equipment. They decided against attempting another engine re-light to preserve battery life. Using a VOR approach procedure found on an Electronic Flight Bag, the crew navigated to Campbeltown, landing safely approximately 40 minutes after the generator failure.
The investigation
The AAIB examined the right engine starter/generator, which had been removed for analysis. The investigation established that the generator armature had sustained damage, including raised bars and damaged brushes, which led to arcing and the subsequent loss of current generation.
Technical analysis suggested that the right engine generator failure was likely caused by latent damage from repeated engine starts with insufficient cooling time between them. This damage likely occurred during the aircraft's period of service with a previous owner, as the current operator had not performed such starts. The damage only became apparent when the generator was subjected to the high load required for an in-flight engine restart.
Findings
- The intentional engine shutdown was part of a planned training exercise to demonstrate one-engine inoperative handling.
- The right engine starter/generator failed due to latent damage to the armature and brushes, likely caused by insufficient cooling between starts during previous operations.
- The failure occurred when the generator was heavily loaded during the attempt to restart the left engine.
- The crew effectively managed the high-workload situation by delegating tasks, such as monitoring battery endurance and performing load shedding.
- The decision to use a VOR approach at Campbeltown was supported by the availability of approach data on the commander's Electronic Flight Bag.