Do you remember the Miracle at Gottröra? Exactly 30 years ago, all 129 passengers and crew survived the crash of an SAS MD-81

Scandinavian Airlines System flight SK751 was a regularly scheduled Scandinavian Airlines passenger flight from Stockholm, Sweden, to Warsaw, Poland, via Copenhagen, Denmark. On 27 December 1991, a McDonnell Douglas MD-81 operating the flight, registration OY-KHO, piloted by Danish captain Stefan G. Rasmussen (44) and Swedish first officer Ulf Cedermark (34), both experienced pilots with 8,000 and 3,000 flight hours, respectively, was forced to make an emergency landing in a field near Gottröra, Sweden. Ice had collected on the wings’ inner roots (close to the fuselage) before takeoff, broke off, and was ingested into the engines as the aircraft became airborne on takeoff, ultimately resulting in the failure of both engines. All 129 passengers and crew aboard survived.

Aircraft

The aircraft was a McDonnell Douglas MD-81, registered OY-KHO with serial number 53003, line number 1844. It made its first flight on 16 March 1991 and was delivered to SAS on 10 April 1991. At the time of the accident, the aircraft had been in service for only nine months. It was fitted with two Pratt & Whitney JT8D low-bypass turbofan engines.

Accident

The aircraft had arrived at Stockholm-Arlanda Airport at 22:09 local time after a flight from Zürich the previous evening and was parked overnight at temperatures of around 0 to 1 °C. About 2,550 kilogrammes of very cold, flight-chilled fuel remained in the wing tanks. Due to this, clear ice had formed on the upper side of the wings, but was not detected. The aircraft was de-iced with 850 litres of de-icing fluid, but not checked afterwards for remaining ice by the de-icing personnel or the pilot-in-charge, captain Rasmussen, which he was required to do by the Scandinavian Airlines “Flight Deck Bulletin/Winterization” given to pilots.

The plane departed from Stockholm at 08:47. Shortly after liftoff, pieces of ice broke off and slammed into the fans of both engines, deforming the fan blades sufficiently to disturb the airflow to the compressors. The disturbed airflow caused the compressors to stall and this, in turn, caused the engines to surge. As the engines were not throttled down sufficiently, the surges continued. The high loads from repeated engine surges quickly led to the breakup of both engines.

From the pilots’ point of view, after 25 seconds of flight, noises and vibrations caused by the No. 2 engine surging were first noticed. The flight crew responded by throttling down a little, but an automatic system, ATR (automatic thrust restoration), that had not been described to the flight crew by SAS, simultaneously increased throttle as a response to the asymmetric engine power and reduced climb rate. As a consequence, the engine surges continued. SAS flight captain Per Holmberg, who was on board as a passenger, noticed the problems early, hurried to the cockpit, and provided invaluable assistance to the crew. Engine No. 1 surged 39 seconds later and both engines failed at 76 and 78 seconds, respectively, into the flight, at an altitude of 3,220 ft.

The pilot responded to the loss of both engines by pitching the aircraft down in a dive before levelling it, to try to have it glide the longest possible distance without stalling. The pilots requested a return to Arlanda and attempted the restart procedure, but, with the aircraft emerging from cloud cover at 890 ft altitude, they chose a field in the forest, near the Vängsjöberg seat farm in Gottröra, Uppland, for an immediate emergency landing.

During the final descent, the aircraft hit several trees, losing a large part of the right wing. It struck the ground tail-first, and the tail cone of the plane broke off. The plane slid across the field for 110 metres, during which the main landing gear of the plane dug marks into the field and sheared off, the nose landing gear broke off, and the fuselage broke into three parts. As a result of the accident, 25 people were injured—two of them seriously—but there were no fatalities. The flight attendants had instructed passengers to adopt the brace position, which is credited with the lack of fatalities.

The flight crew, and especially captain Rasmussen, were lauded for the skilled emergency landing in a fast-developing, potentially fatal situation. Rasmussen commented that “few civilian air pilots are ever put to a test of the skills they have acquired during training to this degree“. He said he was proud of his crew and very relieved everyone had survived. He chose not to return to piloting commercial aircraft.

The incident is known as the Gottröra crash (Swedish: Gottrörakraschen) or the Miracle at Gottröra (Swedish: Miraklet i Gottröra) in Sweden.

Scandinavian Airlines continues to use flight number SK751 for its Copenhagen-to-Warsaw route.

Investigation and recommendations

The conclusion of the official accident report stated:

• “The accident was caused by SAS’ instructions and routines being inadequate to ensure that clear ice was removed from the wings of the aircraft prior to takeoff. Hence the aircraft took off with clear ice on the wings. In connection with liftoff, the clear ice loosened and was ingested by the engines. The ice caused damage to the engine fan stages, which led to engine surges. The surges destroyed the engines.

Contributory causes were:

• The pilots were not trained to identify and eliminate engine surging.

• ATR – which was unknown within SAS – was activated and increased the engine power without the pilots’ knowledge.” [That reminds of the MCAS on Boeing 737 MAX aeroplanes]

In the section “Compressor Failures”, the report stated:

• “With sufficiently reduced thrust in the right engine and maintained thrust in the left, the engines would probably not have failed. The aircraft would then have been able to return for landing.”

Source: Wikipedia