Russian investigators probing a gear-collapse and overrun by a Sukhoi Superjet 100 have determined that the friction coefficient of the Yakutsk runway was far lower than the figure given to the crew.
The Yakutia aircraft had been operating the flight, from Ulan-Ude on 10 October, with its right-hand thrust-reverser deactivated.
While this deactivation was permitted as a deferred item, it meant that the criteria for landing included a runway friction coefficient no lower than 0.4.
The Superjet crew was told that the coefficient for runway 23L was 0.45, according to federal air transport regulator Rosaviatsia’s preliminary findings.
But an assessment of the runway surface revealed the presence of ice, and friction measurements for the various sections of the runway turned up values of 0.25-0.32.
Rosaviatsia says these figure might indicate that the surfaces at Yakutsk airport are “inadequately maintained”. Temperatures at the time of the landing were below freezing.
Construction work on runway 05R/23L had displaced the threshold of runway 05R by 1,150m and reduced the available landing distance of 23L to 2,248m.
Rosaviatsia says the aircraft touched down on 23L but overran by 250m into the area of the runway undergoing reconstruction. As it travelled along the closed surface, the main landing-gear collapsed and the aircraft’s engines and aft structures contacted the ground.
Ninety-one passengers and five crew members were on board, and they evacuated through emergency slides. Four occupants sought medical treatment.
Rosaviatsia says the aircraft’s captain had logged 1,080 on type out of 13,125h in total, while the first officer had 1,300h on type from 3200h.
Superjet manufacturer Sukhoi Civil Aircraft stresses that the deactivated thrust-reverser had “no impact” on the aircraft’s safe operation.
But the state of the runway, it says, with almost half the coefficient of friction than the figure transmitted to the crew, required reconsideration of the decision to land. “The crew of the aircraft, which was not provided with [the actual friction] information, could not prevent the aircraft from rolling off the end of the runway,” it adds.