Date: 03 April, 1996
Operator: United States Air Force [USAF]
Aircraft type: CT-43
Location: 3nm north-west of Dubrovnik Airport [DBV], Croatia
Fatalities: 35 of 35
Relevant weather conditions: IMC
Accident type: controlled flight into terrain
Primary causes: Pilot error, violations.
The following is a human factors analysis of the crash of IFO-21; factual information of the sequence of events is drawn primarily from information provided by the United States Department of Defence [U.S. DoD] (1996a1, 1996b2).
Sequence of events
Unfortunately for the investigators, the CT-43 was not equipped with either a FDC or CVR, which limited knowledge of what was going on in the cockpit. However, Dubrovnik air traffic control provided some valuable information which allowed investigators to put together a picture of what the pilots of IFO-21 did to contribute to the crash. An important point to note is that the passengers of IFO-21 were US officials, including the Secretary of Commerce, and were en-route to a meeting with US and Croatian officials
Incorrect flight plan
The first error was that the pilots' flight plan would take flight IFO-21 into restricted airspace. Well into the flight, when the pilots became aware of this, they were required to spend 15 minutes changing the flight path en-route to avoid this area.
The approach to Dubrovnik was a nonprecision NDB approach, which required the pilots to tune in to two NDBs near the airport. As a result, two ADF receivers were required on board the aircraft, one for each beacon, but the CT-43 had only one, meaning IFO-21 could not even legally fly the approach.
This image shows the NDB approach to DBV, and the course of IFO-21
(Image embedded from Wikipedia on 18 October 2011)
This type of approach was not even approved for Department of Defence aircraft, and should not have been flown even if the CT-43 was equipped with two ADFs.
The approach into Dubrovnik was rushed, as radar information identifies IFO-21 flying at 220 kts instead of the usual 140 kts, almost 60% faster than normal, which was also commenced without a clearance.
The pilots received a radio call from an aircraft which had just landed in front of IFO-21, about seven minutes before the crash, reporting that the weather was deteriorating and near minimums.
The pilots continued with the approach but did not fly it accurately; they were were off course by nine degrees, and passed both the missed approach point and minimum safe altitude before impacting a mountainside 1.7 miles from the runway threshold. There was no indication of trouble prior to the crash, and the crew did not broadcast a mayday.
It was established that the aircraft was mechanically sound, and while low cloud and rain was present at the time of the accident, the weather was not a factor in the accident.
Flying the approach dangerously fast and without a clearance were almost certainly violations as the result of perceived time pressure. Weigmann and Shappell (20013) state that more fatal accidents are associated with violations, as opposed to errors. The violations committed by the crew made this accident very serious from a safety perspective, as the pilots knew they were committing unsafe acts, as opposed to errors or slips which are accidental. It is very important to understand why the pilots decided to make these dangerous decisions that cost 35 lives.
While the pilots may not have normally continued with such a marginal approach, the combination of important passengers travelling to a multi-national meeting and an en-route delay caused the pilots to experience destination obsession, also known as 'get-there-itis', a compelling urge to get to their destination, even in very unfavourable circumstances (Ewing, 20034; Robson, 20085).
Plan continuation bias
When the pilots received the radio call about weather conditions being close to minimums, it may have further hardened their resolve to press on, believing that they may only have one attempt at landing before conditions deteriorated below minimums. After receiving notification about deteriorating weather, the pilots still continued with their approach, even though they had enough fuel to abort the landing and try again. This is an indication of the pilots' destination obsession developing into 'plan continuation bias' as they approached the airport, pursuing their plan to land at Dubrovnik, even with many factors stacked against them, and the possibility of an alternate decision, to go around (Robson, 20085).
It is possible for the pilots to acclimatise to the worsening situation, and even search for excuses to make continuing with their plan seem more acceptable, and the option of going around seem more inadvisable. Unfortunately, the pilots' actions made the accident all but inevitable.
US military transport pilots were poorly prepared to fly nonprecision NDB approaches. In fact, as NDBs are almost non-existent in the US, the crew likely had little experience with these types of approaches.
A series of mistakes and violations made by the crew of IFO-21, coupled with a lack of training and experience on NDB approaches led to this crash. The pilots likely rushed the approach due to the important nature of the flight, and became susceptible to mental mindsets which encouraged the continuation of the doomed approach.