V1 - That critical Sacred Cow.

[Uplinker]

.....which is what I said at post #10

But of course, you might not be aware of engine low thrust if your probes were blocked.

`if you reach 50% distance of the runway available,before reaching 71%Vr,you`d better stop...

A readout of distance to go would not be the best way to present this, since that would require the pilots remembering numbers for the distance at which they must continue etc., and it would add mental processing time and the potential for mistakes - was it 1430m or 1340m ? And watching a display of numbers counting down would require all of one's attention to the detriment of monitoring the engine instruments etc.

A simple large GO appearing on the PFDs and maybe also the EWD at the V1 point would suffice, with the FMS doing all the calculations so the pilots could concentrate on the centre-line and the engine instruments until GO appeared, at which point they must continue the take-off.

The FMS software code for the GO function could also provide a STOP warning if the acceleration was significantly too low between brakes off and V1.

No numbers, and no interpretation required.

[172_driver]

While I appreciate the airmanship of the story presented by the OP it's not an everyday case with faulty instrument readings. A much more common threat is the faulty inputs of weight in the TODC (Boeing OPT, Airbus FlySmart etc). A system that dynamically calculates the latest stopping point still needs the correct input. Same for an expected acceleration feature.

[john_tullamarine]

That is to say, there are no absolute guarantees in certification - only probabilities. Most of the time it works adequately well, most of us would opine very well. Sometimes the pilot really needs to know a bit about the background to make sensible decisions. Sometimes it all goes awry and we all die. So long as the last situation is very remote, I don't think that I'll have many sleepless nights worrying too much about the distant outliers on the distribution curve. After all, we did make it safely to the airport on the roads without getting killed .. and that was, by far, a much riskier process to endure.

[Amadis of Gaul]

Originally Posted by 172_driver

While I appreciate the airmanship of the story presented by the OP...

As do I. I look forward to his next story about how he was a check airman on a Ford Trimotor that managed not to vibrate itself to pieces.

[Someone Somewhere]

Originally Posted by 172_driver

While I appreciate the airmanship of the story presented by the OP it's not an everyday case with faulty instrument readings. A much more common threat is the faulty inputs of weight in the TODC (Boeing OPT, Airbus FlySmart etc). A system that dynamically calculates the latest stopping point still needs the correct input. Same for an expected acceleration feature.

More mass means less acceleration. If you have a given thrust (from engine setting), mass (from crew input), and acceleration (from IRS) but they don't match, at least one of the three must be wrong and you'd know by like 30 knots. No need to count markers or look at speed readout; the IRS will tell you your longitudinal acceleration is 3.75 meters per second per second.

[FullWings]

I think a likely reason (apart from cost and inertia) that we haven’t seen TOPM appear on the flight decks of aircraft from the major manufacturers is that it may be more difficult than it appears to design something that cautions when appropriate but doesn’t give false warnings. What sort of margins are there to play with? Considering that for maintenance reasons, most performance software tries as hard as it can to make a balanced field and that you’d be lucky if the aircraft actually weighed within 1% of what the load sheet said, it might be that the warning envelope would overlap with “normal” operations. Add in the variables of where the aircraft actually starts its takeoff run, contamination, variance in wind and temperature and it might be a non-trivial task to algorithmically discriminate between OK and not so?

[safetypee]

It is important to separate acceleration issues from V1 - control and aircraft performance.
Without probability statistics, coupling accel and V1 generates mind-cluttering uncertainty.

For those of us who can remember the days of Vstop and Vgo for contaminated operations, V1 has safety benefit, and clarity and simplicity in decision making. Unfortunately the latter has been eroded with extreme 'what if' scenarios and the appalling 'except' caveat originating from the US unions.

We should remind ourselves that engine reliability is significantly better than when V1 was a critical issue; also that modern aircraft are generally easier to control and operate.

Over focus on 'system failures' or situations which defy clear understanding or implications may contribute to incorrect choice of action: e.g. as previous observations on 'tyre failure' - how do you know (and any discussion or deduction before replying should take less than 1 sec)

The missing SOP is "I don't know'. We hate uncertainty thus make it up - we justify actions which in hindsight might be judged negatively.

[Centaurus]

Originally Posted by Amadis of Gaul

As do I. I look forward to his next story about how he was a check airman on a Ford Trimotor that managed not to vibrate itself to pieces.

Interesting you mention the Ford Trimotor. While of course that was well before my time, my first boss Harry Purvis AFC flew the Fokker Southern Cross during the 1930's. It was in that era that Sir Gordon Taylor flew the Fokker Tri motor that had an engine failure while flying over the Tasman Sea between New Zealand and Australia. Leaving his copilot to fly the aircraft, Gordon Taylor climbed out over the wing and using a thermos flask transferred the engine oil from the dead engine into the live engine on the other wing which had been using oil at a high rate. I understand he made several trips transferring oil before the aircraft landed at Sydney.

Years later I briefly met Sir Gordon after he landed at Rose Bay flying boat base after flying a Catalina from South America to Australia circa 1950. Harry Purvis was his copilot. For my part I joined the RAAF in 1951 and amongst other types including Mustangs, flew 3000 hours on Lincoln bombers which included over 30 engine failures requiring asymetric landings. The Rolls Royce Merlins on the Lincoln were not all that reliable in the tropics.

[Amadis of Gaul]

Originally Posted by Centaurus

For my part I joined the RAAF in 1951 and amongst other types including Mustangs, flew 3000 hours on Lincoln bombers which included over 30 engine failures requiring asymetric landings. The Rolls Royce Merlins on the Lincoln were not all that reliable in the tropics.

They weren't all that reliable outside the tropics either. Nobody expected them to be around long after the War.

[PENKO]

Originally Posted by hans brinker

I cannot agree more. All the calculations are based on ground run, the decision is based on airspeed instruments, with wild variations in gusty conditions. It should definitely be based on ground based parameters, corrected for wind gust. and acceleration data should absolutely be included.

But isn’t that just two sides of the same coin? Incorrect wind input will degraded your performance one way or another. What good is a GPS based GO call when your airspeed is way below what it actually should be (i.e. windshear causing an unexpected tailwind)?