What happened
On February 26, 2003, an Embraer 145, operated by Tyrolean Airways under registration OE-LSM, was performing a scheduled IFR flight from St. Gallen Altenrhein to Vienna. Shortly after the aircraft climbed to approximately 5,000 feet AMSL, the flight crew observed a "LAV SMOKE" warning illuminate in the cockpit. Simultaneously, an alarm was triggered in the rear lavatories, and a small amount of smoke was detected in the vicinity of the lavatory area.
In response to the warning, the crew elected to abort the flight to Vienna and instead returned to the departure airfield at Altenrhein. During the diversion, there was no requirement for the use of oxygen masks.
The investigation
The Swiss authorities reviewed the circumstances surrounding the smoke alarm and the subsequent flight diversion. Upon assessment, the investigation was discontinued because there was no evidence of a dangerous situation developing on board the aircraft.