What happened
On April 8, 2003, a scheduled passenger flight operated by a domestic carrier was cruising at 27,000 feet en route from Madrid to Jerez de la Frontera when the right-hand windshield suddenly shattered. Prior to the structural failure, the flight crew reported seeing smoke in the upper right corner of the windshield pane and noticed an unpleasant, acrid odor within the cockpit.
In response to the smoke and the broken pane, the crew donned emergency oxygen masks and declared an emergency. The aircraft performed an emergency descent to 14,000 feet before returning to Madrid, where it landed without further damage to the aircraft or injuries to the 6 passengers or the crew.
The investigation
Investigators examined the aircraft's anti-ice and anti-fog systems, which utilize electrically conductive metal oxide layers within the windshield laminates to maintain temperature. Post-incident maintenance inspections revealed that the electrical connectors, made of bakelite, had overheated.
The investigation also reviewed maintenance records, noting that the aircraft had been flagged the previous day for an "irritant" smell in the cockpit, which had been attributed to the air conditioning system. While the aircraft was released for service, the underlying issue with the windshield heating system persisted.
Findings
- The primary cause of the incident was an electrical malfunction in the windshield anti-ice system that led to excessive current consumption.
- This high current caused the overheating of the plastic electrical connectors and the pyrolization of the windshield laminate material, producing smoke and an acrid odor.
- The investigation concluded that the malfunction likely stemmed from one or more loose electrical connections at the upper right corner of the first officer's windshield, potentially due to insufficient torque applied to the connector screws.
- The existing maintenance task, which required checking cockpit windows every 72 flight hours, was insufficient to detect the internal electrical degradation.
- The manufacturer's database indicated a significant history of similar incidents, with approximately 80 similar events recorded in the FAA Service Difficulty Reports database since 1973.
Safety action
- REC 11-03: It was recommended that Boeing provide MD-87 operators with a maintenance letter detailing the symptoms and causes of windshield cracking to prevent future occurrences.