Incidents related to performance calculations
I cite these two previous incidents below simply to show that it is surprising how large an error in performance calcs a crew will accept. (I'm the author of the first of the stories.)
Some posts above have suggested that an error in V speeds of sufficient magnitude to cause this accident was inconceivable. I'm not implying I have any insight into whether this was a factor at Madrid or not - but I do think these incidents make it clear that the notion is not out of the question.
Somebody out there may know whether the procedures/kit used by Spanair are the same as SAS, which I think is likely given their commercial/operational relationship. And you may have opinions on the subtle factors at play with the trend to uplinked weights and/or V speeds.
SAS probes procedures after close call on take-off
Kieran Daly, London (03Sep99, 12:16 GMT, 759 words)
SAS is reviewing its cockpit procedures after a Boeing 767 came close to catastrophe on take-off when the crew used the wrong aircraft weight for its performance calculations.
The captain of the Tokyo-bound 767-300ER aborted take-off at Copenhagen after rotation when he realised something was wrong and managed to stop inside the length of the airport's 3,570m (11,713ft) runway 22R from a speed of around 140kt (260km/hr).
The aircraft suffered a minor tailstrike and burst tyres and it has since been established that the crew had entered the aircraft's zero fuel weight (ZFW) instead of its gross weight - about a 65t difference.
SAS, which recently changed its procedure for calculating take-off speeds - switching from using a hand-held computer in the cockpit to the use of the ACARS (aircraft communications addressing and reporting system) datalink to have the final calculation performed elsewhere - is now trying to see if there is a way to reduce the chance of a repetition.
A senior Captain involved in the review tells ATI: "This happened to a very experienced professional colleague of mine. My first thought was that if this can happen to a solid fellow like this then it can happen to anyone. So we have to look into it and see what we can do."
Another SAS official - director of flight operations in Denmark, Fleming Jeppsson - relates how in the 24 August incident the co-pilot was conducting the take-off and rotated the aircraft at the calculated speed (VR).
Jeppsson says: "The take-off data computation was based on far too low a take-off weight. So that gave a very, very low V1, V2, and VR and when the rotation was performed it did not give the desired results. The aircraft over-rotated and there was a tailscrape although it turned out to be not bad enough to warrant changing the skid.
"The captain realised that something was wrong and told the co-pilot to lower the nose. All the indications told him to carry on, which is what they are told to do, but he realised something was wrong and he aborted the take-off."
Remarkably the aircraft suffered only a scraped tailskid and three of four tyres burst on the left main landing gear, requiring the tyres and brakes to be replaced. Jeppsson says some passengers did not immediately even realise anything was amiss.
The SAS captain explains that since implementing ACARS some six months ago, SAS' procedure on the 767 fleet is for one pilot to enter the data for the calculations into the flight management system datapage and for both pilots to verify the inputs and the results.
The data entered comprises the aircraft's actual gross weight as passed to the crew, the wind, temperature, altimeter setting and runway condition. That is transmitted via ACARS to SAS operations' department and, within about 20s, the calculated flap setting, full thrust, derated thrust if possible, and speeds are transmitted back and printed out in the cockpit.
Before the introduction of ACARS, the SAS 767 fleet was using hand-held "take-off calculators" in the cockpit to calculate the same data - a major advance on the paper charts used by airlines for decades.
The SAS captain says: "The charts gave us very exact but very conservative figures so the calculator was a great step forward and ACARS is even better. I don't think I would want to revert to the old system."
Because the old chart system required the use of very conservative assumptions it actually constrained the loads that aircraft could carry at marginal airports, meaning the switch to computed solutions had a direct effect on operating efficiency.
Both SAS officials confirm that, although the Swedish investigation authorities are examining what happened, there is no question that it was the crew that made the error and not the operations staff.
Jeppsson says: "As soon as we identify the weak area then my idea would be to immediately correct it. But we don’t want to change a procedure or anything like that until we know exactly what we want to do.
"We have sent a message to pilots to say that obviously this is a grey area to put it mildly. It seems like something very basic but clearly it can happen."
What is certain is that SAS would be extremely reluctant to reduce the use of ACARS itself - it has been a hugely enthusiastic user of the system and datalink programme manager, Bjorn Syren, publicly identified its role in take-off calculations as "a big success" at an ARINC symposium in May.
Source: Air Transport Intelligence news
Pilot error blamed for SIA's Auckland tailscrape
Nicholas Ionides, Singapore (16Dec03, 01:08 GMT, 525 words)
A severe tailscrape incident on takeoff involving a Singapore Airlines (SIA) Boeing 747-400 at Auckland International Airport in March was caused by basic crew errors that resulted in a slower-than-required rotation speed, according to New Zealand accident investigators.
New Zealand’s Transport Accident Investigation Commission (TAIC) says in its final report that a takeoff weight transcription error led to a miscalculation of the takeoff data, which resulted in a low thrust setting “and excessively slow takeoff reference speeds”.
It says the rotation speed had been mistakenly calculated for an aircraft weighing 100t less than the actual weight of the 747-400, which suffered substantial damage to its lower rear fuselage.
As a result the rotation speed was 33kt (61km/h) less than the 163kt (302km/h) that was required for the aircraft. When the captain rotated the aircraft for takeoff the tail struck the runway “and scraped for some 490m until the aeroplane became airborne”.
The TAIC says in its report that the 49-year-old captain, who has since left SIA, had 12,475hr of flying experience at the time but only 54hr on the 747-400, as he had just converted from the lighter Airbus A340-300.
One of two first officers on board had 223hr of flying time on the 747-400 and only 1,309hr in total. The other “was a qualified and very experienced first officer”, with around 3,386hr on the aircraft type.
None of the 369 passengers or 20 crewmembers on board the aircraft was injured. The ten-year-old 747-400, registered as 9V-SMT, was operating as flight SQ286 on 12 March 2003, bound for Singapore. The crew returned the aircraft to Auckland after takeoff and made a successful overweight emergency landing.
“The system defences did not ensure the errors were detected, and the aeroplane flight management system itself did not provide a final defence against mismatched information being programmed into it,” says the TAIC.
“During the takeoff the aeroplane moved close to the runway edge and the pilots did not respond correctly to a stall warning. Had the aeroplane moved off the runway or stalled a more serious accident could have occurred.”
It adds: “The aeroplane takeoff performance was degraded by the inappropriately low thrust and reference speed settings, which compromised the ability of the aeroplane to cope with an engine failure and hence compromised the safety of the aeroplane and its occupants.”
The TAIC says “safety recommendations addressing operating procedures and training” were made to SIA, while a recommendation concerning the flight management system was made to Boeing.
Star Alliance carrier SIA says in a statement that the TAIC’s safety recommendations “have been, or are being, implemented in full”, adding that it is “sorry that pilot error prior to the takeoff led to this aviation occurrence”.
“The emergency procedures followed by our pilots led to the aircraft returning to Auckland safely a short time later with no injuries to passengers or crew. The safe return is a reflection of the pilots’ training and good airmanship,” it says.
“We wish to assure our customers that the lessons from this occurrence and arising out of this thorough investigation by the TAIC have been learnt and several procedural changes have already been implemented.”
Source: Air Transport Intelligence news