The Polish accident: circumstances

As more information emerges about the accident flight, it becomes increasingly difficult to understand the justification for its planning and execution in the marginal weather that prevailed.

On 10 April the Polish air force Tupolev Tu154M operating the presidential flight took off from Warsaw for the 800km journey to Smolensk Severny (Smolensk North). The latter is a former air force base, recently decommissioned by the military but now used as Smolensk's sole civil/military airport since the recent closure of nearby Smolensk Yuzhny (Smolensk South).

Smolensk airport has no precision approach aids, and meteorological observations provided there do not meet ICAO specifications. For example they can provide estimated visibility from the control tower, but not runway visual range. There were no special arrangements made for the presidential flight, according to our sources. Three days earlier (7 April) the same aircraft had flown the identical trip carrying the Polish Prime Minster, so the crew of the presidential flght should not have faced any unknowns.

               

The presidential flight was to be carried out in daylight, but fog was forecast at the destination airport. About 90min before the Tu-154 was due to arrive, a Polish air force Special Air Transport Wing Yakovlev Yak-40 carrying journalists landed at Smolensk in fog. About 30min before the presidential flight was expected, a Russian air force Ilyushin IL-96, bound for Smolensk carrying Russian Federal Security Service staff, was ordered to divert because the weather was below minimums. In Russia, air traffic control can give orders to military flights, but both the Polish air force flights had civilian status, so they could only be provided with advice and information.

When an aircraft hits the ground on the approach, it is self-evident that it was lower than it should have been at that point. The answer sought in all approach accidents is why it was too low. The Russian authorities say conversation between the crew and ATC was normal, and the pilots did not report any technical problems. Initial scans of information from flight recorders also suggests no problems with the aircraft.

If that is the whole truth, we are in the familiar realms of human factors.

If a pilot is determined to land from an approach in marginal conditions, it is tempting for him/her to continue descent below the minimum descent height (MDH) for the approach aid in use, hoping to see the runway through the fog, and relying on seeing the ground below the aircraft so as to avoid collision with it. In the case of the presidential flight, according to air transport regulator Rosaviatsia's chief, Alexander Neradko, the aircraft was so low that it hit an 8m high tree when still 1,200m from the runway threshold. At that point on a standard 3deg approach glideslope it should still have been at 60m height, says Neradko.

But whatever the height of a theoretical glideslope at 1,200m, this flight should not have descended even as low as 60m (182ft) on this approach without the pilots being able to see the runway - and with the reported visibility being 400-600m in fog, they could not have done. The airport has no precision approach aids, and the status of the aids it has have not been confirmed by the authorities yet.