Misunderstandings

Forum for discussing non-Pakistani aviation issues and news.


smhusain_1
Registered Member
Posts: 217
Joined: Sat Jul 19, 2008 6:16 pm
Location: Brampton, Ontario, Canada

Misunderstandings

Post by smhusain_1 » Mon Jun 09, 2014 1:37 am

VATYA SAà MUCHACHO?¬“ OVERSHOOTEZ! OVERSHOOTEZ!*
*Agitated exchange between Brazilian pilots and French controllers

"TCAS, satellites and ASD are expensive gadgets for the “fat cats of aviation--“speech costs nothing, but its careless usage can cost lives. The problem is as old as aviation itself. That it has been allowed to grow as old as that is almost criminal. In 1971, it was still allowed in Sydney that aircraft should taxi, backtracking on the runway that was also in use for landings and take-offs. On a clear but dark night, a DC 8 landed. The controller instructed the pilot to "take Taxiway Right, call on 121.7". This was acknowledged with “roger" but not read back.
Eventually, the four-man cockpit crew (all from another English-speaking country!) would declare unanimously that what they heard was “backtrack if you like, change to 121.7". They made 180 degrees turn and started back down the runway. The controller thought he saw the DC 8 turn on to the taxiway nearby, and cleared a 727 for take-off. There was a collision, but somehow, nobody got hurt. It is not impossible to mishear take taxiway right as “backtrack if you like", and the accident report acknowledged that accent and idiom might have contributed to the misunderstanding. But had the pilot given or the controller demanded a proper read-back of the instruction, the danger would have never arisen.

In 1974, A BOAC 747 (call sign Speedbird 029) was approaching Nairobi. Its controller was working under supervision, but the supervisor left the room for four minutes during which a clearance was issued to the aircraft: "Speedbird zero two nine . . .descend seven five zero zero feet. The QNH is one zero two zero decimal five." The pilots heard “five zero zero zero feet and that was what the co-pilot read back fast and without hesitation: "Roger Speedbird zero two nine cleared five thousand feet on one zero two zero decimal five." The mistake was not spotted, and the acknowledgement was not challenged by either the flight engineer on board or the radar controller because, as it often happens, both might have heard what they expected to hear. It is probable that the word “seven" was indistinct, the “five" was given greater emphasis, and the pilots were concentrating on counting the zeroes. Setting their target height, the pilots now had a chance to pick out the error: 5,000 feet is 500 feet below ground level at Nairobi! There were, however, slight problems in the cockpit. The crew, on duty for nine hours, was at the “lowest point of their normal circadian rhythmic cycle because at home they would now be asleep. The co-pilot had a bowel infection for which he had treatment from his own doctor without informing the airline, and the medication might have reduced his efficiency just when he might have been keen to impress a very senior captain of great repute with whom he was flying for the first time. Perhaps he acted briskly, without pause for thought which might be interpreted as indecision. The captain tended to do too much by himself, GPWS was not yet employed, the company monitoring system, which would soon have to be improved, was not followed properly, and some instrument indications of the problems were overlooked or ignored. When the aircraft broke through the clouds -- and the co-pilot shouted: “Give full power . . . give full power! . . . Check height! The ground was coming up at them at 217 knots. By the time they managed to climb away, they were only seventy feet from impact. If one tried at this stage the worst tragedy with the biggest toll on record, one would need the computer power behind the Voyager space venture, and the outcome would still be dependent on a timely puff of wind or someone deciding to ask a pilot “what did you say?"

On March 27, 1977, two Jumbos were heading for Las Palmas in the Canary Islands. Both were on time. The PanAm came from Los Angeles, the KLM from Amsterdam. But at the airport a bomb explosion was followed by the threat of another, so all incoming flights were diverted to Los Rodeos airport at nearby Tenerife. There the runway centre lights happened to be out of order yet again, the runway intersections were not lit or even marked properly, and the weather was playing one of its treacherous tricks, a local peculiarity, with drifting fog that would produce dramatic changes of visibility from one moment to the next. The airport was soon overcrowded with diverted flights. As the PanAm had pulled up just before the KLM, it got hemmed in at the end of a parking area.

Waiting, waiting, everybody itched to go and make the short hop to Las Palmas. The controllers waited to see the back of them all. The KLM was meant to return to Amsterdam the same evening. The pressure was on the pilots: their duty-time would be exceeded, and everybody would be stranded overnight if they could not leave Tenerife pretty soon. When at long last the “all clear came from Las Palmas, the weather deteriorated, and the KLM captain decided to refuel in case he could not get into Las Palmas after all. That held up the American pilots who knew that their 380 tired passengers were keen to start their twelve-day luxury cruise. They walked impatiently around the Dutch plane to measure if there was enough room on the apron to squeeze through and go first, but the gap was too narrow. They just had to wait.
The two Jumbos would have priority to leave, but the taxiways were still chock-a-block with parked aircraft, diverted aircraft. As both captains were ready to depart, the tower gave them permission to taxi almost in tandem, backtracking on the main runway. The KLM would go to the far end, turn back, and take-off. The PanAm would follow it but only as far as the third intersection where it would turn off, and hold. There was some confusion in both cockpits. The Americans were unsure which intersection they were supposed to find in the fog. That was sorted out, but they had only a small map of the unfamiliar airport, and they missed the unmarked turn-off. Still, they could take the next exit.
The KLM crew rushed through their pre-take-off checklists as they taxied down the runway. They wanted to finish the job in hand, so they delayed asking for their route clearance until they reached their take-off position. They were already lined up and keen to roll when the co-pilot warned the captain “to wait a minute because they had not yet received their route clearance. (That was already a little more interference than the co-pilot was keen to exercise: his captain was not only very senior to him, not only the face in company advertisements, but also the chief KLM flying instructor who had type-rated him, and who, therefore, must be right at all times). The captain told him to get the clearance. The scene was now set for some transmission congestion.

The Tower reeled off the route to follow after and subject to take-off clearance. While the co-pilot was reading back, the brakes were released, and the captain increased power. The crew overheard the communications with the PanAm flight giving rise to some doubts concerning the whereabouts of the other Jumbo. The flight engineer asked repeatedly: “Is hij er niet af die Pan American?(Is he off, the PanAm?). The answer he received from the captain was an emphatic but most ambiguous “Jawe" (Yes). The co-pilot ended his read-back with the non-standard, meaningless words: “We're now at take-off." The controller did not ask for any clarification because he interpreted that to mean that the KLM was now at the point from where it would be ready to leave as soon as the second, the vital take-off clearance was granted*

*Spanish, American and Dutch investigators who listened, eventually, to the voice recording agreed that the co-pilot's words would not imply anything like taking off without further ado.

So he just said “Okay, which in itself was incorrect. But two seconds later, perhaps a little bothered by that peculiar sentence, he added: “Stand by for take-off. I will call you. He did not know that the actual take-off procedure had been initiated some six seconds earlier.
The PanAm crew did not like the sound of what they heard. All that talk about take-off . . . Lost and insecure in the soup, they chose to warn the other pilot directly. The simultaneous radio transmissions coming into the KLM cockpit now caused a temporary blocking of the frequency as they fused into a four second shrilling squeal. The word “take-off” had been mentioned. Raring to go, and under the influence of anticipation, the Dutch captain longing to hear that clearance must have turned wishful thinking into reality and the 747 began to accelerate.

The Americans could not see the aircraft bearing down on them through the fog, but sensed the menace. “Let's get the hell out of here”, said the captain; Co-pilot: “Yeh, he's anxious, isn't he?”; Captain: “There he is . . . look at him . . . goddam . . . that son of a bitch is coming!”

The PanAm tried to turn and get out of the way. When the KLM captain saw the obstacle in his path, he had two seconds to save himself. He yanked at the wheel, and tried desperately to get airborne. The excessive rotation managed to lift the nose, but the tail just dragged along scraping the runway. The collision could not be averted. Almost 100,000 liters of fuel poured out of the ruptured tanks. The whole airfield seemed to be afire.
All 248 souls aboard the KLM perished. Seventy of the 306 people on the PanAm flight emerged from the inferno alive, but all survivors were badly injured, and nine of them would soon swell the death toll to 583. The investigators clearly blamed the captain who had taken off without clearance and disregarded both doubts and instructions. (A Dutch inquiry insisted the circumstances and coincidences should exonerate the crew). The old culprits or “inadequate language” and the ready acceptance of non-standard communications were named prominently among the factors which had contributed to the tragedy.

Forerunners, repetitive errors, that painful ring of familiarity? There is no end to them. Fatigue, stress and noise play havoc with eager expectations. That is how sprinters on the track or competitors in a swimming pool jump the gun and make a false start. That is how it is easy to fall prey to selective hearing, like a military pilot who absorbed only cleared . . .for take-off out of cleared into position and hold, standby for take-off; or the captain who misheard the non-standard phrase clearing him to “runway 09 holding position and read back “runway 09, hold in position, which ought to have been picked out by the controller “ that is the point of the exercise" but the man in the tower, anticipating no more than a echo of his own words, failed to spot the slight change. The problem is that even trained crew finds it difficult positively to expect the worst, i.e. mistakes all the time, and therefore a chasm can often be often be found between read back and hear back. Misunderstandings can occur anywhere in a similarly innocent fashion.

Reading is usually more infallible than listening, and yet in the course of turning peacefully the pages of a book, undisturbed by noise, adverse circumstances or the monotony of monitoring, one can glance at the first words of a well-known proverb and overlook the misprint. . . A BIRD IN THE THE HAND THE HAND is no reason to search for errors or expect to see any.

Airborne misunderstandings work the same way. As reported to CHIRP, a British aircraft in U.S. airspace received the instruction to continue climbing to six zero. The word to was somewhat elongated by the usual heavily accented growl, and so the co-pilot confirmed, "continue climbing two six zero". The difference was a mere 20,000 feet, and, on its mistaken way up, the British flight barely avoided a very close encounter with another aircraft. Even the standard, ICAO approved phrase, "Line up and wait" has produced confusions when pilots heard it "Line up one eight".
It is a daunting fact that seventy per cent of the fifty thousand safety reports in the NASA database involve some oral communication problem.
At Tenerife, an apparently innocuous exchange between Tower and PanAm pilots could have created a fatal trap for the KLM captain. The squeal in the cockpit blanked out a PanAm transmission but, one second after the noise had ended, the controller said: “Papa Alpha one seven three six report runway clear. It was audible in the KLM cockpit, but was it a statement in Pidgin English or a request? If it was taken as a statement, the Dutch crew might have stopped the conscious effort to listen any more to chit- chat that seemed to be none of their business. The PanAm answer was okay, will report when we're clear,' but would the busy KLM crew fully absorb any but the anticipated last words" we're clear?

Excerpts from: Final Call by Stephen Barlay, Sinclair & Stevenson Ltd., London UK, 1990

“It is difficult for most people to understand how anyone as experienced as the Dutch captain could have made an error of such magnitude. For those used to regular hours and familiar surroundings, with nights asleep in their time zone and frequent rest periods, it may be impossible to comprehend. But the flying environment, although for the most part routine, can place great strain on an individual. Constant travelling in alien environments, long duty days, flights through the night and irregular rest patterns can all take their toll. The Dutch crew had been on duty for almost 9 ½ hours and still had to face the problems of the transit in Las Palmas and the return to Amsterdam. Lack of recent route experience for the captain, especially in these trying conditions, did not help. The pressure was on to leave Los Rodeos as early as possible and the weather was not making it easier. A gap in the drifting cloud had presented itself and the captain had taken the opportunity to depart. Close concentration was required on the take-off as clouds were once again reducing visibility. At such moments the thought process of the brain can reach saturation point and become overloaded. The ‘filtering effect’ takes over and all but urgent messages, or only important details of the task in hand, are screened from the mind. Radio communications which were being conducted by the first officer were obviously placed in low priority in the minds of both the pilots once the takeoff had been commenced. The controller’s use of papa alpha instead of Clipper – the only occasion that day on which the identification was used – reduced the chances of registering the transmission.”

Air Disasters by Stanley Stewart published in England by Ian Allen in 1986.