Rapid Cabin Decompression on a Boeing 737-31S Near Erfurt

Incident Overview and Flight Details On June 22, 2001, a commercial Boeing 737-31S operated by an airline was conducting a scheduled flight from Munich to Hamburg. The aircraft was carrying five crew members and 126 passengers. During cruise at flight level 350, the cabin experienced a sudden rapid decompression with a rate exceeding 2,000 feet per minute. The cabin altitude indicator showed 10,000 feet and was rising. ## Crew Response and Outcome Oxygen masks deployed automatically and were used by the occupants. The crew initiated an emergency descent to flight level 100. No injuries were reported among the passengers or crew. The crew decided to continue the flight to the destination airport at flight level 100. The subsequent flight and landing in Hamburg were completed without further issues. ## Investigation and Findings To determine the cause, the aircraft owner conducted a ferry flight to Munich at flight level 90 with the pressurization system inoperative. During troubleshooting, defects were found in two pressure seal clamps that seal the APU air duct penetrations outside the cabin. One clamp at the aft pressure bulkhead had slipped off the sealing sleeve, while the second clamp in the main wheel well area was broken. After repositioning one clamp and replacing the other, followed by functional tests, the aircraft was returned to service. ## Company-Wide Inspection and Root Cause Following the incident, the airline inspected all its Boeing 737 aircraft. It was found that the majority of the fleet had clamps that were not tightened sufficiently. Two aircraft exhibited the same defects that caused the incident on June 22, 2001. The company assessed that the defects were largely attributable to production issues at the manufacturer. The locations where the clamps failed were outside the manufacturer's maintenance planning document control requirements. ## Safety Recommendations The German Federal Aviation Accident Investigation Office (BFU) issued safety recommendation 10/2001, advising the German Federal Aviation Office (LBA) to request all operators of Boeing 737 aircraft within its jurisdiction to perform detailed visual inspections of the pressure seal clamps at the APU air duct penetrations in the aft pressure bulkhead and main wheel well areas.