What happened
On the night of January 25, 2001, a US-registered Piper PA-34-220T was conducting an instrument flight rules (IFR) flight from Biggin Hill, England, to Augsburg, Germany. The aircraft was carrying a pilot and four passengers. The flight was intended to conclude with an ILS approach to runway 25.
During the descent, the aircraft was being radar-guided by Munich Center. While the pilot was assigned a heading of 220° to intercept the localizer, the aircraft's course changed to approximately 250°. This deviation caused the aircraft to drift roughly 0.72 NM to the right of the approach centerline. At 21:24 local time, the aircraft flew into hilly terrain prior to reaching the runway threshold. The impact and subsequent fire destroyed the aircraft. The pilot and three passengers were killed, while one passenger sustained serious injuries.
The investigation
The BFU investigation examined radar recordings, radio communications, and the aircraft's avionics configuration. Investigators analyzed the coordination between Munich Center and the Augsburg tower, as well as the pilot's workload and the aircraft's navigation settings. The investigation also reviewed the visibility conditions and the availability of ground-based navigation aids during the final approach.
Findings
Several critical factors contributed to the accident. The primary cause was that the GPS remained the active signal source for the Horizontal Situation Indicator (HSI) during the intended ILS approach, which suppressed the glide slope indication. Because the pilot was unaware that the glide slope information was unavailable, the descent was not managed according to the required minimum descent altitude (MDA) for a glide slope-inoperative approach.
Contributing factors included:
- A significant lateral deviation from the approach centerline occurred, which was not detected by the pilot and was not communicated by air traffic control.
- The aircraft's cockpit design featured poorly positioned and illuminated GPS/NAV switches, making it difficult for the pilot to monitor the active navigation source.
- There was a lack of coordination between the various air traffic control units involved.
- The pilot was experiencing high workload following a long duty day, which hindered the recognition of the altered approach characteristics.
- The aircraft lacked an automatic direction finder (ADF) and did not utilize a second ILS indicator to monitor the approach.