That’s just over complicating things. If the margins are so tight that the thrust needs to be nudged up during the take-off roll then you shouldn’t be flying. The performance data LSL is talking about has a certain amount of safety factor built in. The data we use in our type only accounts for half of the reported head wind so if you use the 10 knot headwind column to get your figures it’s really based on 5 knots of headwind, so it doesn’t matter if the wind is gusting around a bit. For the tail wind columns it accounts for 1.5 x the reported tail wind, so if you use the 10 knot tail wind column you are good with gusts up to 15 knots. The aeroplane has been shown to be able to achieve a certain gross climb gradient with an engine failed, but that gross gradient is artificially reduced to account for degradation of airframe and engines and less than perfect piloting technique.
So you go to the book and see how much thrust you need for the weight you are at for that take-off. The thrust setting is expressed in terms of one of the engine instruments on the flight deck. For us it is N1 which is the speed of the first fan in the engine, others use EPR which is the pressure ration between the engine intake and the exhaust.
Then you line up and set the N1 you need. If you are flying something built in the last 20 years or so you might be able to push the TOGA buttons and have the autothrottle set the thrust for you. Then you roll down the runway. If anything goes wrong prior to some arbitrary relatively slow speed (air speed), 80 knots for us, then it’s ok to abort the take-off. If you are between 80 knots and V1 then you ONLY abort for a major failure such as an engine failure or something that may affect the ability of the aeroplane to fly. After V1 you go regardless of what happens. You are normally better off carrying a failure into the air than attempting a high speed abort. If you have an engine failure after V1 then you continue the take-off, climbing the aeroplane to a safe height. You will have a company produced escape procedure that keeps you safe from obstacles while you climb away. Once safely up in the air you sort out the problem and decide what to do next. Probably you will burn off fuel down to your landing weight and then come back.
As **Richard Pearse **said, the industry could, in theory, do all this. To very little gain in safety or economics for a major increment in complexity. But something vaguely similar is coming, which I’ll describe below.
For brevity in the previous post I omitted to mention that there is a lower limit to permissible takeoff thrust. Or said another way, there’s a maximum permissible reduction from full thrust. The details vary between various aircraft types, but broadly speaking, taking the maximum reduction means we’re taking off at about 70% of full thrust. Given the typical runways, weather, and mission loads, many many takeoffs are made at the minimum thrust / maximum reduction setting. Which provides performance well in excess of just barely clearing the 3 safety criteria.
Assuming that lower limit isn’t changed, more detailed real-time calcs won’t accomplish anything.
At various times in the past there have been attempts to quantify expected acceleration and develop a procedure to verify that performance is as expected early enough in the takeoff roll to safely correct the situation. Aborts from even moderate speeds are dangerous and expensive, so you need a procedure which has a very low false alarm rate. Having the crew verify that by point X on the runway we’ve achieved speed Y didn’t meet that criteria and has faded from use.
There are efforts underway now to add real time acceleration monitoring. Not thrust adjustment, just monitoring. The present certification standards require all automation to be disconnected from actual engine control during takeoff; the risk of an automation or instrumentation malfunction causing a power reduction is judged more severe than the benefits of fine-tuning thrust.
Overall, modern airplanes are pretty highly engineered machines. But a lot of what happens in daily operations follows the old saw of “measure it with a micrometer, mark it with a crayon, and cut it with an axe.”
The vagaries of time-compressed activities in less-than-laboratory conditions on an industrial scale with seven 9’s reliability standards require that at least some things be done in the simplest manner possible (but no simpler), with a sufficient safety pad for the statistically inevitable times when the axe cuts to the right of the crayon mark which is to the right of where the micrometer measured.