Aircraft Information
The aircraft involved was an Agusta A109 AII helicopter, registration I-DPCA. It was built in 1985 by Agusta and powered by two Detroit Diesel Allison 250-C20B engines. The helicopter had a maximum takeoff weight of 2600 kg and a cruising speed of 120 knots. It was registered in 1986 with a valid certificate of airworthiness. The last periodic inspection was performed on 12 August 2004, with zero flight hours since then.
Event Description
On 14 August 2004, at 10:40 local time (08:40 UTC), the helicopter was conducting a transfer flight from Caiolo (Sondrio) to the Elilario base in Colico. The flight was part of a post-maintenance acceptance procedure. While flying at approximately 1000 feet AGL over an area near S. Pietro Berbenno (SO), the right rear emergency exit door detached unintentionally. The area was sparsely populated and used for agriculture. A subsequent low-altitude search using the onboard GPS did not locate the missing component.
Investigation Findings
Examination revealed that the door seals were correctly installed at the time of the event, and the hinge pin seats on the sliding door structure showed no damage. The door is secured by two fixed pins at the top that insert into corresponding holes on the door frame, and two lateral pins operated by emergency handles located inside and outside the passenger door. The closing sequence includes a locking mechanism with a spring-loaded detent. This locking feature had previously been evaluated as inadequate by Agusta, leading to the issuance of mandatory Technical Bulletin 109-95 on 28 February 1994 (later embodied in AD RAI 94-71) after a prior similar in-flight loss. The bulletin required verification of correct handle positioning, locking pin engagement, and periodic inspections every 100 flight hours. The maintenance organization confirmed compliance with this bulletin during the last inspection on 12 August 2004. However, because the door was not recovered, the exact cause could not be determined definitively.
Probable Cause
The probable cause is attributed to an accidental rotation of the emergency exit door handle, likely induced by normal in-flight vibrations and resulting from a locking mechanism that probably did not meet the technical standards.