THE US AIR FORCE Boeing T-43A (737-200) which crashed on 3 April on approach to Dubrovnik, killing US Commerce Secretary Ron Brown, was using a single, relatively primitive non-precision navigation aid in weather which was significantly worse than forecast, the USAF has revealed (Flight International, 10-16 April).
When the aircraft hit a 2,300ft (700m) cloud-covered ridge some 1km (0.5nm) off the approach track, all 35 people on board the aircraft were killed, including Brown and a deputation of senior US industrialists.
Dubrovnik's runway 12 approach, is flown either visually or using a pair of non-directional beacons (NDBs), in line with the runway's extended centre-line. The first is 22km from the runway and the second is a locator beacon at the 3km-to-go point.
The airport's instrument landing system had been ripped out by departing Yugoslav soldiers in 1991 and never replaced. NDBs, the simplest and least accurate of navigation beacons, with no capacity for giving range information, are less common in developed nations, but still frequently used globally.
The aircraft, however, had only one automatic direction-finder (ADF) receiver (the device for displaying the NDB's direction relative to the aircraft), so the crew could not use both beacons as a check.
The USAF says that the beacons appeared to be serviceable.
The aircraft was not fitted with any global-navigation-satellite system, says the USAF.
Visibility for the airport was forecast to be 13km, although it was 8km. The cloud-base was predicted to be 25,000ft, when it was 2,000ft (300ft lower than the ridge), says the USAF. The cloud-base was 1,000ft lower than the minimum published for the approach.
Source: Flight International
