Aborting a take off because of a feeling something is not right
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Aborting a take off because of a feeling something is not right
This thread is allied to the ATSB report on the King Air accident at Essendon. Mods may decide to move it to that thread or leave it here as a separate discussion.
The ATSB report states in part: There was insufficient evidence to determine why the pilot delayed rotation from 94 kt to 111 kt or why the take-off was not rejected.
Essendon Runway 17 had a potentially deadly overrun into the Tullamarine Freeway if the aircraft is not stopped by the end of the existing overrun area. This writer has previously advocated Essendon airport authorities seriously consider additional aircraft stopping measures in the form crushed material beyond the runway end particularly where an over-run could lead to fatal consequences to aircraft occupants and those caught in the way. See:https://en.wikipedia.org/wiki/Engine...rrestor_system No interest was shown by the relevant authority.
The take off roll of the KingAir was longer than normally expected and the delayed rotation proved this. Some sources questioned why the pilot did not abort the take of roll once it became clear that he was having problems with directional control approaching 94 knots the nominal rotation speed. Unless there is a definite indication of a serious problem during the takeoff roll such as fire warning, a more subtle indication such as the aircraft pulling slightly to one side may be interpreted by the pilot as something vaguely amiss but he doesn't have sufficient marked cues to make the critical decision to abandon the take off roll. Two examples using real incidents may illustrate this.
Firstly: https://www.fss.aero/accident-report...9-09-20-US.pdf
A Boeing 737-400 started its take off roll with the F/O as PF. The crew were unaware that an electrical fault had moved its rudder trim from neutral to full scale left. The rudder trim had been confirmed at neutral before engine start. It takes 29 seconds for the rudder trim to move from neutral to full scale in one direction. The only clue would be a slightly offset rudder pedal position which could easily go unnoticed. During the early part of the take off run the aircraft started to drift left of the runway centreline; enough to concern the PF which he voiced to the captain. With the aircraft accelerating, a short discussion took place between the two pilots culminating in the captain taking over full control. He was able to track back towards the centreline and made the decision to abort but did not commence the abort procedure including reverse thrust and braking, until on the centreline. Earlier in the beginning of the take off roll there was a delay before full power was selected due to a problem with the autothrottle selection. That delay used up more runway. The result was the aircraft overran the far end and went into a river causing fatalities.
In short, the combinations of uncertainty caused initially by the aircraft gradually veering to the left and getting worse as speed picked up, followed by a delay before the captain took control and then his slow actions with regard to stopping the aircraft, all led to the fatal overrun. But it all started with a feeling that something was not quite right early in the take off roll. The King Air pilot at Essendon no doubt had a similar feeling that something was not quite right; but by the time things were getting serious in terms of directional control and VR approaching, the presence of the Tullamarine Freeway right off the end of the runway may have influenced his decision to keep flying rather than risk a high speed abort.
Example No. 2
The feeling that something wasn't quite right was evident in this case during a midnight take off in a 737-200 from the 5600 feet length runway on Nauru island in the Central Pacific Region.. There was no overrun area for Runway 30. There was however, a road five metres away and a cliff covered with boulders and then the ocean. Readers may be familiar from Air Disaster TV videos, of the Air Florida 737 crash into Washington's Potomac River. See: https://en.wikipedia.org/wiki/Air_Florida_Flight_90
On that occasion ice had blocked the sensors to engines power indicating instruments (EPR) resulting in the crew thinking they had full power when the actual power was much less than planned. The aircraft used the full length of runway and hit a bridge shortly after lift off and crashed into the river.
In the case of the 737 incident at Nauru, it wasn't ice that blocked the sensors and thus gave erroneous high power engine instrument indications, but instead a combination of phosphate dust from nearby mines and insects that had blocked the thrust sensors. The result was the same in that the 737 used all the runway because of lower power than expected. Because it was a night takeoff and therefore a more difficult perception of distance remaining, it wasn't until the last 200 metres of runway and airspeed well below V1, that it suddenly became evident the aircraft would not get airborne before the end of the runway. The captain's decisive actions to manually apply full available throttles to the stops and carefully rotate at the extreme end, saved the day (or night in this case). The jet exhaust blast lifted parts of the adjacent road back on to the runway. It was the closest shave of this writers career. I know this because I was in the jump seat praying the captain would not abort and finish over the cliff and into the sea. There was lots of sharks in the area.
In each of the examples given, there was a vague feeling on the flight deck that something wasn't quite right early in the takeoff roll but not enough evidence that an abort was warranted. All the engine instruments looked normal in that needles were all parallel and in expected positions. But in the early part of the take off roll a keen eye would have picked a slight discrepancy between expected EPR (engine pressure ratio) and actual engine N1 or RPM indications. In the case of the Nauru incident, all three of us in the cockpit missed the warning signs. But that is being wise after the event.
Referring back to the King Air Essendon accident. One can now perhaps understand the human factors aspect of the pilot's decision to keep on going when he probably only had a vague idea that something wasn't quite right early during his takeoff roll but couldn't pin it down until too late to abort knowing there was a potentially fatal overrun on to the Tullamarine freeway below.
The ATSB report states in part: There was insufficient evidence to determine why the pilot delayed rotation from 94 kt to 111 kt or why the take-off was not rejected.
Essendon Runway 17 had a potentially deadly overrun into the Tullamarine Freeway if the aircraft is not stopped by the end of the existing overrun area. This writer has previously advocated Essendon airport authorities seriously consider additional aircraft stopping measures in the form crushed material beyond the runway end particularly where an over-run could lead to fatal consequences to aircraft occupants and those caught in the way. See:https://en.wikipedia.org/wiki/Engine...rrestor_system No interest was shown by the relevant authority.
The take off roll of the KingAir was longer than normally expected and the delayed rotation proved this. Some sources questioned why the pilot did not abort the take of roll once it became clear that he was having problems with directional control approaching 94 knots the nominal rotation speed. Unless there is a definite indication of a serious problem during the takeoff roll such as fire warning, a more subtle indication such as the aircraft pulling slightly to one side may be interpreted by the pilot as something vaguely amiss but he doesn't have sufficient marked cues to make the critical decision to abandon the take off roll. Two examples using real incidents may illustrate this.
Firstly: https://www.fss.aero/accident-report...9-09-20-US.pdf
A Boeing 737-400 started its take off roll with the F/O as PF. The crew were unaware that an electrical fault had moved its rudder trim from neutral to full scale left. The rudder trim had been confirmed at neutral before engine start. It takes 29 seconds for the rudder trim to move from neutral to full scale in one direction. The only clue would be a slightly offset rudder pedal position which could easily go unnoticed. During the early part of the take off run the aircraft started to drift left of the runway centreline; enough to concern the PF which he voiced to the captain. With the aircraft accelerating, a short discussion took place between the two pilots culminating in the captain taking over full control. He was able to track back towards the centreline and made the decision to abort but did not commence the abort procedure including reverse thrust and braking, until on the centreline. Earlier in the beginning of the take off roll there was a delay before full power was selected due to a problem with the autothrottle selection. That delay used up more runway. The result was the aircraft overran the far end and went into a river causing fatalities.
In short, the combinations of uncertainty caused initially by the aircraft gradually veering to the left and getting worse as speed picked up, followed by a delay before the captain took control and then his slow actions with regard to stopping the aircraft, all led to the fatal overrun. But it all started with a feeling that something was not quite right early in the take off roll. The King Air pilot at Essendon no doubt had a similar feeling that something was not quite right; but by the time things were getting serious in terms of directional control and VR approaching, the presence of the Tullamarine Freeway right off the end of the runway may have influenced his decision to keep flying rather than risk a high speed abort.
Example No. 2
The feeling that something wasn't quite right was evident in this case during a midnight take off in a 737-200 from the 5600 feet length runway on Nauru island in the Central Pacific Region.. There was no overrun area for Runway 30. There was however, a road five metres away and a cliff covered with boulders and then the ocean. Readers may be familiar from Air Disaster TV videos, of the Air Florida 737 crash into Washington's Potomac River. See: https://en.wikipedia.org/wiki/Air_Florida_Flight_90
On that occasion ice had blocked the sensors to engines power indicating instruments (EPR) resulting in the crew thinking they had full power when the actual power was much less than planned. The aircraft used the full length of runway and hit a bridge shortly after lift off and crashed into the river.
In the case of the 737 incident at Nauru, it wasn't ice that blocked the sensors and thus gave erroneous high power engine instrument indications, but instead a combination of phosphate dust from nearby mines and insects that had blocked the thrust sensors. The result was the same in that the 737 used all the runway because of lower power than expected. Because it was a night takeoff and therefore a more difficult perception of distance remaining, it wasn't until the last 200 metres of runway and airspeed well below V1, that it suddenly became evident the aircraft would not get airborne before the end of the runway. The captain's decisive actions to manually apply full available throttles to the stops and carefully rotate at the extreme end, saved the day (or night in this case). The jet exhaust blast lifted parts of the adjacent road back on to the runway. It was the closest shave of this writers career. I know this because I was in the jump seat praying the captain would not abort and finish over the cliff and into the sea. There was lots of sharks in the area.
In each of the examples given, there was a vague feeling on the flight deck that something wasn't quite right early in the takeoff roll but not enough evidence that an abort was warranted. All the engine instruments looked normal in that needles were all parallel and in expected positions. But in the early part of the take off roll a keen eye would have picked a slight discrepancy between expected EPR (engine pressure ratio) and actual engine N1 or RPM indications. In the case of the Nauru incident, all three of us in the cockpit missed the warning signs. But that is being wise after the event.
Referring back to the King Air Essendon accident. One can now perhaps understand the human factors aspect of the pilot's decision to keep on going when he probably only had a vague idea that something wasn't quite right early during his takeoff roll but couldn't pin it down until too late to abort knowing there was a potentially fatal overrun on to the Tullamarine freeway below.
Last edited by Centaurus; 27th Sep 2018 at 15:34.
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Well composed Centy:-) Re the B737 with the rudder trim fault I wonder why a take off config warning wasn't forthcoming during the application of power? Might be other conditions that precluded that. I knew Max & having thousands of Hrs on type myself I am perplexed at what happened & certainly don't subscribe to the ATSB's end report, something doesn't add up, that's just a cop out! We may never know the real truth, just assumptions is all the pilot community is left with sadly:-(
As for your thread subject? Well there is no one answer or feeling to continue or abort. In some ways transport cat A/C make that decision somewhat simpler but it's never an exact science. Gee there is still two camps as to what the meaning of V1 is & what to do at that exact speed? Personal flying experience, gut feeling butterfly's in yr tummy all help make that decision to stop or go. The human factor in all this is so vague, we can make a 100 airframes exactly the same right down to the toilet flush button colour but we will NEVER make a 100 pilots the same, there in lies the real issue so we have to just accept that accidents are all part of the risk of flying.
As for your thread subject? Well there is no one answer or feeling to continue or abort. In some ways transport cat A/C make that decision somewhat simpler but it's never an exact science. Gee there is still two camps as to what the meaning of V1 is & what to do at that exact speed? Personal flying experience, gut feeling butterfly's in yr tummy all help make that decision to stop or go. The human factor in all this is so vague, we can make a 100 airframes exactly the same right down to the toilet flush button colour but we will NEVER make a 100 pilots the same, there in lies the real issue so we have to just accept that accidents are all part of the risk of flying.
Gee there is still two camps as to what the meaning of V1 is & what to do at that exact speed?
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Re the B737 with the rudder trim fault I wonder why a take off config warning wasn't forthcoming during the application of power?
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It's often heard, both versions, even some Airlines I believe have diff interpretations as to what V1 should be! It's know as the 'Decision speed', that statement alone is open for interpretation!
machtuk, what the reg says.
(1) VEF is the calibrated airspeed at which the critical engine is assumed to fail. VEF must be selected by the applicant, but may not be less than VMCG determined under §25.149(e). (2) V1, in terms of calibrated airspeed, is selected by the applicant; however, V1 may not be less than VEF plus the speed gained with critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognizes and reacts to the engine failure, as indicated by the pilot's initiation of the first action (e.g., applying brakes, reducing thrust, deploying speed brakes) to stop the airplane during accelerate-stop tests.(b) V2MIN, in terms of calibrated airspeed, may not be less than—
(1) 1.13 VSR for—
(i) Two-engine and three-engine turbopropeller and reciprocating engine powered airplanes; and(ii) Turbojet powered airplanes without provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed;(2) 1.08 VSR for—
(i) Turbopropeller and reciprocating engine powered airplanes with more than three engines; and (ii) Turbojet powered airplanes with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed; and(3) 1.10 times VMC established under §25.149. (c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by §25.121(b) but may not be less than—(1) V2MIN; (2) VR plus the speed increment attained (in accordance with §25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and(3) A speed that provides the maneuvering capability specified in §25.143(h).(d) VMU is the calibrated airspeed at and above which the airplane can safely lift off the ground, and con- tinue the takeoff. VMU speeds must be selected by the applicant throughout the range of thrust-to-weight ratios to be certificated. These speeds may be established from free air data if these data are verified by ground takeoff tests.(e) VR, in terms of calibrated airspeed, must be selected in accordance with the conditions of paragraphs (e)(1) through (4) of this section
1) VR may not be less than—
(i) V1;
(ii) 105 percent of VMC;
(iii) The speed (determined in accordance with §25.111(c)(2)) that allows reaching V2 before reaching a height of 35 feet above the takeoff surface; or
(iv) A speed that, if the airplane is rotated at its maximum practicable rate, will result in a VLOF of not less than —
(A) 110 percent of VMU in the all-engines-operating condition, and 105 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition; or
(B) If the VMU attitude is limited by the geometry of the airplane (i.e., tail contact with the runway), 108 percent of VMU in the all-engines-operating condition, and 104 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition.(2) For any given set of conditions (such as weight, configuration, and temperature), a single value of VR, obtained in accordance with this paragraph, must be used to show compliance with both the one-engine-inoperative and the all-engines-operating takeoff provisions.(3) It must be shown that the one-engine-inoperative takeoff distance, using a rotation speed of 5 knots less than VR established in accordance with paragraphs (e)(1) and (2) of this section, does not exceed the corresponding one-engine-inoperative takeoff distance using the established VR. The takeoff distances must be determined in accordance with §25.113(a)(1).(4) Reasonably expected variations in service from the established takeoff procedures for the operation of the airplane (such as over-rotation of the airplane and out-of-trim conditions) may not result in unsafe flight characteristics or in marked increases in the scheduled takeoff distances established in accordance with §25.113(a).(f) VLOF is the calibrated airspeed at which the airplane first becomes airborne.
(g) VFTO, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by §25.121(c), but may not be less than—
(1) 1.18 VSR; and
(2) A speed that provides the maneuvering capability specified in §25.143(h).
(h) In determining the takeoff speeds V1, VR, and V2 for flight in icing conditions, the values of VMCG, VMC, and VMU determined for non-icing conditions may be used.
§25.107 Takeoff speeds.
(a) V1 must be established in relation to VEF as follows:(1) VEF is the calibrated airspeed at which the critical engine is assumed to fail. VEF must be selected by the applicant, but may not be less than VMCG determined under §25.149(e). (2) V1, in terms of calibrated airspeed, is selected by the applicant; however, V1 may not be less than VEF plus the speed gained with critical engine inoperative during the time interval between the instant at which the critical engine is failed, and the instant at which the pilot recognizes and reacts to the engine failure, as indicated by the pilot's initiation of the first action (e.g., applying brakes, reducing thrust, deploying speed brakes) to stop the airplane during accelerate-stop tests.(b) V2MIN, in terms of calibrated airspeed, may not be less than—
(1) 1.13 VSR for—
(i) Two-engine and three-engine turbopropeller and reciprocating engine powered airplanes; and(ii) Turbojet powered airplanes without provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed;(2) 1.08 VSR for—
(i) Turbopropeller and reciprocating engine powered airplanes with more than three engines; and (ii) Turbojet powered airplanes with provisions for obtaining a significant reduction in the one-engine-inoperative power-on stall speed; and(3) 1.10 times VMC established under §25.149. (c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by §25.121(b) but may not be less than—(1) V2MIN; (2) VR plus the speed increment attained (in accordance with §25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and(3) A speed that provides the maneuvering capability specified in §25.143(h).(d) VMU is the calibrated airspeed at and above which the airplane can safely lift off the ground, and con- tinue the takeoff. VMU speeds must be selected by the applicant throughout the range of thrust-to-weight ratios to be certificated. These speeds may be established from free air data if these data are verified by ground takeoff tests.(e) VR, in terms of calibrated airspeed, must be selected in accordance with the conditions of paragraphs (e)(1) through (4) of this section
![Frown](https://www.pprune.org/images/smilies/sowee.gif)
(i) V1;
(ii) 105 percent of VMC;
(iii) The speed (determined in accordance with §25.111(c)(2)) that allows reaching V2 before reaching a height of 35 feet above the takeoff surface; or
(iv) A speed that, if the airplane is rotated at its maximum practicable rate, will result in a VLOF of not less than —
(A) 110 percent of VMU in the all-engines-operating condition, and 105 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition; or
(B) If the VMU attitude is limited by the geometry of the airplane (i.e., tail contact with the runway), 108 percent of VMU in the all-engines-operating condition, and 104 percent of VMU determined at the thrust-to-weight ratio corresponding to the one-engine-inoperative condition.(2) For any given set of conditions (such as weight, configuration, and temperature), a single value of VR, obtained in accordance with this paragraph, must be used to show compliance with both the one-engine-inoperative and the all-engines-operating takeoff provisions.(3) It must be shown that the one-engine-inoperative takeoff distance, using a rotation speed of 5 knots less than VR established in accordance with paragraphs (e)(1) and (2) of this section, does not exceed the corresponding one-engine-inoperative takeoff distance using the established VR. The takeoff distances must be determined in accordance with §25.113(a)(1).(4) Reasonably expected variations in service from the established takeoff procedures for the operation of the airplane (such as over-rotation of the airplane and out-of-trim conditions) may not result in unsafe flight characteristics or in marked increases in the scheduled takeoff distances established in accordance with §25.113(a).(f) VLOF is the calibrated airspeed at which the airplane first becomes airborne.
(g) VFTO, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by §25.121(c), but may not be less than—
(1) 1.18 VSR; and
(2) A speed that provides the maneuvering capability specified in §25.143(h).
(h) In determining the takeoff speeds V1, VR, and V2 for flight in icing conditions, the values of VMCG, VMC, and VMU determined for non-icing conditions may be used.
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[A Boeing 737-400 started its take off roll with the F/O as PF. The crew were unaware that an electrical fault had moved its rudder trim from neutral to full scale left. The rudder trim had been confirmed at neutral before engine start. It takes 29 seconds for the rudder trim to move from neutral to full scale in one direction. The only clue would be a slightly offset rudder pedal position which could easily go unnoticed. During the early part of the take off run the aircraft started to drift left of the runway centreline; enough to concern the PF which he voiced to the captain. With the aircraft accelerating, a short discussion took place between the two pilots culminating in the captain taking over full control. He was able to track back towards the centreline and made the decision to abort but did not commence the abort procedure including reverse thrust and braking, until on the centreline. Earlier in the beginning of the take off roll there was a delay before full power was selected due to a problem with the autothrottle selection. That delay used up more runway. The result was the aircraft overran the far end and went into a river causing fatalities.
How many B737 pilots actually understand how their rudder trim works? Boeing doesn’t help too much in the manual to be honest.
The answer is, in practicality, all the rudder trim does in a 737 is displace the rudder pedals. That is an excellent engineering design, because it draws immediate attention to the pilot that the trim is in place - providing the pilot has their feet on the rudder pedals.
It is also immediately overridable, merely by centreing the rudder pedals, and this does not require much force. It also does not limit full opposite rudder operation. A 737 could takeoff with full left rudder trim, suffer a left engine failure near V1, and reject or takeoff quite safely.
The only clue would be a slightly offset rudder pedal position which could easily go unnoticed.
Given what we now understand as to the function of rudder trim in a B737, which was it? Full runaway trim as stated in the report would result in full (or close to full) rudder pedal displacement. I would assume that no respected 737 pilot would advance to takeoff thrust without his feet on the rudder pedals, and if he had his feet there surely he would have immediately noticed the anomaly. I restate my fascination with the above report.
P.S. I note you have provided a link to the full report. I have not read it yet.
Last edited by Derfred; 29th Sep 2018 at 16:33.