Preliminary information about the Boeing 747-400F crash at Bishkek appears to indicate that the aircraft encountered a false glideslope before initiating its fatal descent, and that the crew attempted a go-around.
The information is contained in a detailed formal communication – the authenticity and nature of which FlightGlobal has yet to verify – and states that the aircraft, on a Category II ILS approach, crossed a final approach point some 650ft above the published height of 3,400ft. This approach point was around 3.2nm (5.9km) from Bishkek Manas's VOR and some 7.4km before runway 26.
It says this error had resulted from inadequate altitude checks by the crew.
The aircraft had captured the localiser but was unable to capture the glideslope because it was too high and, following its initial descent, it levelled off at 3,400ft as directed by the ‘altitude hold’ mode.
ILS antenna transmissions can create a false mirror glideslope above the normal 3° approach path, at steeper slopes including 6° and 9°.
As the aircraft reached a point 1.5km from the runway threshold – in the vicinity of the Manas VOR – it briefly encountered the 9° false glideslope, activating its glideslope capture mode.
The document narrative states that the 747 began to descend on a 3° slope in parallel to the genuine glideslope, adding that the crew did not realise that a safe landing from an altitude of 3,400ft – over 1,300ft above the airport elevation – would have been “impossible” from a distance of just 1.5km.
Nor did the crew, it says, notice that the glideslope indicator on the primary flight display was set in its lowest position, signalling a large deviation.
As the aircraft descended it overflew the entire runway until, at the decision height of 100ft, the captain opted to execute a go-around owing to an absence of visual ground references.
But the go-around mode, with take-off thrust, was only activated at a height of 52ft. In the process of executing the go-around, the aircraft struck the ground 900m beyond the end of the runway and 60m to the right of the extended centreline.
None of the four crew on board the MyCargo Airlines 747, operated by ACT Airlines, survived, and the accident also claimed 35 fatalities on the ground as the aircraft careered into a village on 16 January.