Investigators in Russia have issued a preliminary cause of the Moscow crash of the Sukhoi Superjet 100, which tragically claimed the lives of some passengers and crew.
Summary of the accident
The Sukhoi Superjet 100 Aeroflot flight SU 1492 proceeded with an unstable final approach with wind shear warnings and unstable glideslope indications.
Failing to act on several opportunities for a go-around from the unstable final approach the airplane also landed overweight by 1.6 tons (3,200 pounds).
The bounce and final touchdown impacts were so hard that they caused a force in excess of 5 G’s (G means Gravity) of stress on flight SU 1492’s airplane.
Those were the initial findings from the flight data recorder pulled from the Aeroflot airliner after the May 5 accident.
Here you can see a new Moscow airport video of SU 1492 from the tragic accident:
Rosaviatsia preliminary findings
Rosaviatsia, the Russian Federal Air Transport Agency (FAA equivalent), in coordination with the Russian Air Transport Agency (NTSB equivalent) issued a report of the chain of events that led to the crash. This after analyzing the flight recorder details.
Chain of events that led to the accident of SU 1492
The chain of events that led to the accident are gradually escalating in severity, based on the preliminary findings by the Russian authorities.
After takeoff from Moscow
The airplane was affected by an electrical failure at 8,900 feet. This occurred approximately 5 minutes after takeoff from runway 24C.
Thunderstorm activity was reported in the area. Rosaviatsia did not report anything about the airplane being hit by a lightning strike.
The autopilot and the autothrottle then disengaged.
The standard instrument departure pattern, named KN 24E, was being followed after departure.
The pilots did an air-return to Moscow.
Not being able to communicate via normal radio frequencies the crew was only able to use the VHF emergency frequency. The transponder code used for loss of communication was also transmitted. The flight proceeded with vectors given by air traffic control, hand-flown by the pilot.
Approach to Moscow
A manually-flown ILS approach to runway 24L was then made back into Moscow’s Sheremetyevo Airport.
According to Rosaviatsia the take-off weight of the Sukhoi Superjet was 43.5 tons (87,000 pounds).
The glideslope entry on the ILS approach had the airplane at 42.6 tons (85,200 pounds). That made the airplane 1.6 tons (3,200 pounds) overweight for landing.
The approach was initially stable with an up to 30 degrees left crosswind. Airspeed was 155 to 160 knots.
Unstable final approach
- Five predictive wind shear warnings were triggered during the final approach at 1,100 thru 900 feet above ground level.
- At 260 feet and 180 feet, the airplane was dipping below the glideslope, triggering a glideslope warning alert.
Instead of commanding a go-around at the indication(s) of an unstable approach the pilot chose to proceed to land.
Below the glideslope reactions
The reaction to the below the glideslope alerts was executed by an alternating thrust increase and decrease. Throttle angles changed between 24 and 18 degrees. This occurred as the airplane descended down to 40 feet above the ground.
Airspeed increased to 164 knots above the runway threshold, increasing to 170 knots 16 feet above the ground before touchdown.
When the pilot retarded the throttles to idle he applied pitch attitude adjustments (corrections). The adjustments were between 6 degrees nose up and 2 degrees nose down.
The touchdown that ended with the crash
The plane seemed to be close to touchdown about 700 meters (2,296 feet) from the runway threshold (beginning of the runway).
At about 900 meters (2,952 feet) down the runway, the airplane first touched down in a three-point touchdown. This occurred at 158 knots at a more than 2.5 G’s impact.
A three-point touchdown is where the two main wheels, one set of wheels under each wing, touch the ground at separate times during landing. The nose wheel touches down last after the two mains are on the ground.
Then the plane bounced up to about six feet.
Autospoilers did not deploy.
Spoilers are the surfaces popping up on top of the wing after touch down to create drag. They are also called speed brakes.
Two seconds later the nose wheel hit the runway first, at a 155 knots speed. The G-impact on this one was 5.85 G’s.
The airplane then bounces a second time. This time to 18 feet.
The third and final touchdown was at 140 kts, with a G-impact of about 5.
The structural damage to the airplane caused a fuel spill and the following fire that ensued.
Decelerating through 100 knots sliding down the runway, fire alarms were triggered:
The aft cargo compartment fire alarm first sounded, followed by the Auxiliary Power Unit (APU) fire warning, which happened 16 seconds later.
The engines (PowerJet SaM146) continued running for a while after the crash.
The pilots of SU 1492
According to Rosaviatsia the captain had 1,570 hours of flight time on the
Sukhoi Superjet 100. His total flight time logged was 6,844 hours.
The first officer (co-pilot) had 623 hours of flight hours on the Sukhoi Superjet 100. No first officer total flight time experience information was provided.
Airplane # RA-90098
The accident-airplane had flown 2,710 hours since new, accumulating 1,658 cycles (take off and landings).
Aeroflot SU 1492 Fatalities
A statement by Rosaviatsia indicates that 40 out of the 73 passengers and one crew member did not survive.
Six passengers and three members of the crew were injured.
Featured image: Aeroflot, RA-89098, Sukhoi Superjet 100-95B. Sukhoi.