A potential miscalculation of the fuel loaded onboard the controversial SAA flight that collected Covid-19 vaccines from Brussels will be central to an investigation conducted by the Civil Aviation Authority.
It was just minutes after flight SAA 4272 took off from OR Tambo International Airport on February 24 when the Airbus A340-600 experienced an “Alpha Floor Event”.
An “Alpha Floor Event” is when an aircraft either on takeoff or landing does not have enough thrust and goes into a stall.
Onboard computers on Airbus aircraft are designed to automatically take control and prevent the plane from crashing.
Such incidents are meant to be reported to the regulator within 24 to 72 hours of the event.
CAA spokesperson Kabelo Ledwaba said the regulator was only informed three weeks after the incident.
A source with knowledge of the incident says when the “Alpha Floor Event” happened the aircraft was about 150m above the ground.
“The onboard computers immediately took control of the aircraft. The pilots would have immediately known that something was wrong.
“They would have noticed the nose of the aircraft dipping and then rising quickly as a sudden surge of power came from the engines to build up enough speed so it could complete its takeoff properly.”
He said indications were that the incident occurred because the pilots and aircrew underestimated the weight of the aircraft “by 90 tons”.
“That is a massive underestimation and can carry catastrophic consequences. Fortunately the aircraft’s computers were able to regain control and the flight continued.”
The source said such a weight underestimation was likely to have come from a miscalculation of the fuel load.
“When takeoffs are calculated data such as the outside temperature, runway length and fuel load are all inputted into the onboard computer. The data is check, rechecked and then checked again.
“These pilots and crew are experienced. They are not newbies. This has a lot of people worried. The investigation is going to have to look at how the error of miscalculating 90 tons crept in.
“For now it seems like potential human error, but whose error it is is unknown. Was it something that occurred because the crew were given the wrong information on the fuel load, or was it that the crew themselves simply made the mistake?”
Aviation analyst Guy Leitch said an aircraft’s commander was expected to double-check and then recheck all the figures.
“Airbus A340-600 has a known bug in its software that occasionally allows incorrect data into the flight management system, but this is why the aircrew are required to double check all calculations.
“It is extraordinary to get the weight of the aircraft wrong by a full 90 tons. That is not a small weight. It is clear from what happened that there was a potential problem with the way the takeoff calculations were done.”
He said every time aircraft took off, the aircrew calculated how much thrust was needed for the aircraft to safely take off.
“The calculations are done on flight planning computers, which is usually done by the pilot who is not flying that leg of the journey. That pilot then passes the calculations to the flying pilot, who independently verifies them. These calculations are critical to successful takeoffs and flights. It’s vital that both pilots verify the calculations.
“It is clear a failure occurred on this flight.”
He said such an aircraft weighed roughly 300 tons.
“The crew would have underestimated the aircraft’s weight by nearly a third.”
Leitch said increasingly there was a steady stream of such incidents and accidents occurring globally where pilots had miscalculated an aircraft’s takeoff parameters.
He said it was worrying that the CAA had only been notified three weeks after the incident.
“When the incident occurred, the computers would have sent out automated alerts to SAA, Airbus and the engine manufacturers, Rolls-Royce, who all have 24-hour monitoring systems in place.
“These alerts will include data on the aircraft’s speed, altitude and position along with hundreds of other readings and parameters including temperatures and thrust.”
Airbus spokesperson Samsana Ismail referred all questions related to SAA operations to the airline.
SAA said it would be releasing a statement later.
Ledwaba said they were investigating the incident and the time frame in which it was reported to the CAA.
“The incident report was reported to the SACAA and the Accident and Incident Investigation Division on the evening of 17 March. The event flight took place on the 24 February 2021.
“On receipt of the report, an investigation team was established to probe the incident as well as the reason for the delayed notification to the regulator or the AIID. The regulations stipulate that: aviation accidents must be reported within 24 hours, serious incidents within 48 hours and incidents within 72 hours.”
