What happened
On a flight from Stephenville to St. John's, a Beech 1900D operated by Air Labrador experienced a sudden loss of cabin pressure while climbing through 18,500 feet. The event, which involved two crew members and nine passengers, began with a loud bang and immediate physical symptoms for the crew, including ear discomfort and dizziness. Following the failure of a right-side cabin emergency exit window, the crew performed a rapid descent. The aircraft returned to Stephenville and landed safely at 0900 Newfoundland daylight time with no injuries.
The investigation
Investigators examined the aircraft and found that a significant portion of the right cabin emergency exit window and interior trim were missing. Analysis of the remaining window fragments and adjacent windows revealed surface chip gouges that exceeded the manufacturer's maximum allowable depth of 0.015 inches. Specifically, some gouges were found to be as deep as 0.028 inches, with internal cracking vents visible under magnification.
The investigation also reviewed the crew's response to the depressurization. While the first officer donned an oxygen mask, the captain did not don his own mask, nor was passenger oxygen deployed. Furthermore, the crew's use of emergency checklists was inconsistent, as the captain directed the first officer to use a door-related checklist rather than the appropriate cabin decompression checklist.
Findings
- The exterior surfaces of the failed window and adjacent windows contained chip gouges that exceeded the allowable maintenance tolerances.
- The window failure likely resulted from a cracking failure caused by the excessively damaged condition of the exterior surface.
- The damage was likely caused by debris from a runway surface being thrown against the windows by the propeller wash during a previous takeoff.
- The crew's failure to adhere to standard operating procedures (SOPs) regarding oxygen mask usage and emergency checklists increased the risk of hypoxia and operational errors.
Safety action
Following the incident, the operator replaced several cabin windows with multi-ply versions and updated their inspection protocols. The company transitioned from using a needle-tip dial indicator to an optical micrometer for more precise measurements and increased the frequency of window inspections from 1,200 hours to 200 hours. Additionally, Transport Canada initiated a review of the operator's standard operating procedures and high-altitude training.