Kam Air 737 Crash — A GPS Trap?

Air Safety Week, Feb 14, 2005

With the rescue operation of the Kam Air Boeing 737 that crashed in Afghanistan on Feb. 7 over, the investigation into why the plane crashed has begun. NATO-led troops and Afghan soldiers who reached the wreckage at 11,000 feet found human remains but no survivors.

The 737, on its way from the western Afghan city of Herat, lost contact with air traffic control on its approach to Kabul airport as it flew into a heavy snowstorm. Kabul (and Bagram to the north) sit in a "bowl" that pushes into the Hindu Kush, the lowest point of which is roughly 14,000 feet above mean sea level (AMSL). Snow isn't rare in the area, however snowfall as heavy and intense as seen on Feb. 3 is. Kabul city sits some 6,000 feet AMSL and snow in the mountains tends to be permanent this time of year. Terrain to the far north east rises to 20,000 feet plus, and Kabul has no radar. Flying there is challenging in poor visibility, let alone snowstorms. Kabul runs with Special Visual Flight Rules (SVFR) on days of low visibility. Practically, it means a 10-minute procedural separation between arriving or departing traffic in the zone. The air controllers there are locals, but they are quite sharp and professional and the SVFR system seems to work.

The initial theory for the cause of the crash of the B737 from ex-FAA inspectors on site is that the aircraft was attempting to shoot the VOR (very high frequency omnidirectional range) approach in IMC (instrument meteorological conditions), but was using the database coordinates for the VOR, not the VOR radial itself. The VOR was originally located in the city to the south of the airport, but was moved northeast onto the airport centerline. As a cost-saving move, the designator and frequency of the beacon were not changed. The B737 crew may have programmed the approach into the FMS (flight management system), and with the aircraft having an expired navigation database, had the aircraft fly to the GPS position (global positioning system) of the old beacon, putting them five miles south of the genuine inbound course.

As they were also 1,000 feet below the published approach height, they may have been low on the approach in preparation for the steep descent required on crossing "into the bowl." (Just informed speculation for the moment). Alternately, if they were using the VOR radial for their GPS departure tracking (diversion to Pakistan), a similar scenario could have unfolded.

Afghanistan Visual Flight Rules

Civil flights must be carried out in accordance with the visual flight rules (VFR) as specified in ICAO Annex 2 and 11. Civil flights shall operate in daylight hours only. Compliance with these procedures does not relieve pilots of their responsibility to see and avoid other aircraft or for maintaining safe terrain/obstacle clearance at all times. All civil [aircraft] are restricted to DAY VFR Only Operations operating to/from destinations within the Kabul FIR. All military [aircraft] operating under a ISAF Callsign may maneuver during hours of darkness. Landings after sunset will be restricted to qualified NVG [night vision goggles] crews. Take-offs are at the discretion and training of the crew after all risk assessment has been done.

Source: U.S. Department of Defense Enroute Supplement

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