Polish air force commander Lt Gen Andrzej Blasik has ordered the service's remaining EADS Casa C-295 tactical transports to be grounded until further notice while an investigation takes place into the cause of a crash on 23 January.
The Polish defence ministry says all four crew members and 16 passengers on board the C-295 died when the aircraft - assigned to the air force's 13th Air Transport Squadron - crashed into a forest about 1.7km (1nm) short of the runway at Miroslawiec air base.
Aircraft 019 had been flying a planned course from Warsaw to Krakow via the air force's bases at Powidz, Poznan-Krzesiny, Miroslawiec and Swidwin, and was carrying delegates returning from an annual aviation safety conference in the Polish capital. Among those killed were high-ranking officers including base and squadron commanders and technical chiefs from several air force units.
The accident happened at 19:07 local time, when the cloud base at Miroslawiec was 295ft (90m), visibility was 3km and there was a haze over the airfield. According to air traffic control reports, the aircraft's pilot performed a go-around because of lack of visibility of the airstrip, but during the second approach, reported: "I see the airstrip."
The Polish air force confirms that the base's instrumented landing system was faulty at the time of the crash, restricting the pilot to using only the precision approach radar, but it adds: "The malfunction of the ILS was not a reason for the crash."
Aircraft 019 was one of the newest transports delivered to the Polish air force, and had logged more than 300 flight hours since entering service last August. It was one of 10 C-295s to have entered Polish service since 2003, and its loss is the first involving the Spanish-designed type.
Polish examples have so far logged more than 9,500 flight hours, including 4,500 flown last year, and late last year the service confirmed an order for two more of the aircraft.