Impeded descent preceded 747’s false glideslope crash

[Ref Flight International Magazine 17-23 Mar 2020]

Occurrence Date/Time 16 January 2017 (at night)
Aircraft Type 747-400 freighter
Flight / Operator Turkish Airlines  TK6491
POB  4 crew
Description The aircraft had been maintaining 18,000ft and was cleared to descend to 6,000 ft within 27nm (50km) distance. However, the airline’s standard descent procedure would only have enabled the 747 to lose 9,000ft rather than the required 12,000ft in such a short distance.

Despite the requirement for a more aggressive loss of altitude, the inquiry says the initial descent was conducted without the use of speedbrakes, and with increasing airspeed – this was adjusted to 270kt, then to 280kt, and again to 290kt as the aircraft passed through cloud at 16,000ft.

Some 1min 40s into the descent the crew changed to vertical speed mode and increased the descent rate to 2,400ft/min. The airspeed continued to rise, reaching a maximum of 317kt.

Speedbrakes were deployed manually at 12,200ft – initially to 30° and then to 36° – and the flight level change mode was re-engaged.

The aircraft continued to descend but reached only 9,200ft by the time it passed TOPKA. It was also travelling at 270kt, above the 250kt limit dictated by ACT for flight below 10,000ft.

The 747 automatically followed an incorrect descent path that took it over the airport

Result The 747 landed (crashed) beyond the runway in a residential area, resulting in the loss of all 4 crew members as well as 35 fatalities on the ground.
Contributory factors The absence of speedbrake deployment at the beginning of the descent in the given short distance to lose altitude.

The aircraft remained above the approach profile as it neared Bishkek and inadvertently captured a falseglideslope from the ILS to runway 26.


Recommendation extend the landing-gear eariler, and deployed suitable of flap while keeping the speedbrakes extended, and reduced airspeed to 210kt in order to achieve a steeper descent.

Pilot should be well trained!

Pilot should be vigilance always!


Read More –

ILS – Instrument Landing System

Leave a Reply

Your email address will not be published. Required fields are marked *