What happened
On 16 March 2005, a Bombardier CRJ200, registration D-ACHH, was operating a scheduled passenger flight from Cologne to London Heathrow Airport. While the aircraft was cruising at an indicated airspeed of 250 knots, the Engine Instrument and Crew Alerting System (EICAS) triggered a "SMOKE CARGO" warning.
In response to the alert, the crew initiated the required emergency procedures as outlined in the Quick Reference Handbook. They briefed the passengers and cabin crew before notifying Air Traffic Control to coordinate a priority ILS approach to Runway 27L. Upon landing at Heathrow, the aircraft stopped immediately after exiting the runway to allow for an expedited disembarkation. Airport fire services attended the scene to inspect the cargo hold; however, their investigation revealed no evidence of smoke, fire, or heat damage.
The investigation
The AAIB examined the circumstances surrounding the warning, noting that D-ACH to H had experienced four previous instances of cargo smoke warnings. The investigation looked into the reliability of the smoke detector design and the impact of environmental factors. It was noted that while an airworthiness directive had previously mandated the replacement of older detector units with a revised design intended to resist dust and electromagnetic interference, this newer design had not prevented the recurrence of warnings on this specific aircraft.
Findings
- The cargo smoke warning was almost certainly a false alarm.
- The alert was likely triggered by the smoke detector reacting to dust, condensation, or electromagnetic interference.
- The detector operates by reflecting light off particles; therefore, any dust or moisture within the detection chamber can trigger the sensor.
- Previous studies indicated that while the new detector design aimed to reduce susceptibility to such factors, it remained vulnerable to high moisture content in cargo and electromagnetic interference from devices such as mobile phones or handheld radios.