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Acceleration check procedure for liners

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Acceleration check procedure for liners

Old 12th Aug 2019, 10:35
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Acceleration check procedure for liners

Time and again after incidents like the S7 at Domodedovo, I wonder if during T/O liners donít have any sort of acceleration check or similar procedure, to confirm that the engines are performing as expected during the first stage of the T/O run.

In my ďoutfitĒ (I know, I know, totally different kind), we do a TOLD calculation prior every flight. This calculation will amongst other things show the expected rotation and T/O speed, T/O distance and acceleration check speed.

The acceleration check speed will normally be calculated for a distance of 1000í from brakes release. The 1000í normally equals the distance to the first distance to go marker (normally only present on military fields), but any other visible or displayable feature will work (intersection, distance from mark point generated at brakes release position). The TOLD calculation takes the following data into account: Power setting (MIL or A/B T/O), weight, temperature, pressure, wind, runway conditions (friction, slope, length).

If the expected speed is not reached (+/- 5 KTS in MIL and +/- 10 KTS in A/B) when passing the ref. point, or if rotation or T/O speed is not reached at the expected point, T/O is to be aborted (A/B, provided there is enough RWY left) or full A/B is to be selected (MIL).

This method gives an early indication if all is well, or if the pilots should increase thrust/abort. In cases like the S7, where the wrong weight is put into the system, it will be perfectly clear by the lack of proper acceleration. There most be something like this in the civil world, or?
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Old 12th Aug 2019, 11:13
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Itís effectively the same thing in a transport Aircraft, but itís reliant in all cases on the validity of the data input.
I use a good rule of thumb that works most times as a gross error check. Ultimately in Mil or Civ service we operate for the most part by numbers, but you canít replace experience and the seat of the pants either.
BTW, my old bang seat Jet was underpowered with both engines in reheat!
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Old 12th Aug 2019, 11:18
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The trend vector on the PFD should give a clue as well. They also didn't use full length apparently,
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Old 12th Aug 2019, 12:21
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Originally Posted by Monarch Man View Post
Itís effectively the same thing in a transport Aircraft, but itís reliant in all cases on the validity of the data input.
I use a good rule of thumb that works most times as a gross error check. Ultimately in Mil or Civ service we operate for the most part by numbers, but you canít replace experience and the seat of the pants either.
BTW, my old bang seat Jet was underpowered with both engines in reheat!
You must have been flying the Jaguar !

In the V force we did an acceleration time check to 100 knots.

Much later I suggested a system which I named TOPIS, Take Off Performance Indicating System and the concept was published in the Internationl Journal Of Air Safety many years ago. Basically the display, driven by the FMC was to drive a bug on the ASI giving the required speed. Any significant shortfall required a stop.

I thought Emirates was pursuing such a system, which modern electronics should make easy, after their take off incident at Melbourne, due I believe, to the wrong weights being entered in the FMC
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Old 12th Aug 2019, 12:54
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Originally Posted by RetiredBA/BY View Post

You must have been flying the Jaguar !

In the V force we did an acceleration time check to 100 knots.

Much later I suggested a system which I named TOPIS, Take Off Performance Indicating System and the concept was published in the Internationl Journal Of Air Safety many years ago. Basically the display, driven by the FMC was to drive a bug on the ASI giving the required speed. Any significant shortfall required a stop.

I thought Emirates was pursuing such a system, which modern electronics should make easy, after their take off incident at Melbourne, due I believe, to the wrong weights being entered in the FMC
The fog of time has dulled my memory but I recall we did something similar on the Jag along with a distance remaining or used check.
Far more critical however was having a place to aim the jet at should one of the afforementioned fuel to noise convertors decided to go into quiet mode.
On the B777 at EK in my time there we used a Boeing provided onboard performance tool or OPT which worked very very well, but as ever it required careful data input and cross-checking.
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Old 12th Aug 2019, 13:40
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Originally Posted by Monarch Man View Post
Itís effectively the same thing in a transport Aircraft, but itís reliant in all cases on the validity of the data input.
Wrong data input, weight for instance, will show in a different speed when passing the ref. point. Thats way I asked, as the procedure we use will show either poor engine performance or wrong data input in time to abort the T/O. Only thing I can see is if wrong data input is used on more than one parameter (weight and temperature for instance). Then there is a chance they will cancel each other out with regard to acceleration check speed, but then the T/O speed will be off.
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Old 12th Aug 2019, 17:38
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IIRC the result of previous mind-melts was that due to wide spread of weights and thrust settings (down to 60% rated) a system or method that is simple enough for pilots to understand and dependably reliable is impossible to devise.

The idea is sound, just that the solution was not found.

Last edited by FlightDetent; 13th Aug 2019 at 13:14.
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Old 12th Aug 2019, 18:39
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Originally Posted by F-16GUY View Post
Wrong data input, weight for instance, will show in a different speed when passing the ref. point. Thats way I asked, as the procedure we use will show either poor engine performance or wrong data input in time to abort the T/O. Only thing I can see is if wrong data input is used on more than one parameter (weight and temperature for instance). Then there is a chance they will cancel each other out with regard to acceleration check speed, but then the T/O speed will be off.
Wrong flap setting?
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Old 12th Aug 2019, 19:03
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Originally Posted by gearlever View Post
Wrong flap setting?
Not possible in the F-16. Flaps up/down follows the gear handle. Taking off with the gear and flaps up will probably require one more engine :-)

Doesn't liners have warning systems for wrong T/O configuration?
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Old 12th Aug 2019, 19:16
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Originally Posted by F-16GUY View Post
Not possible in the F-16. Flaps up/down follows the gear handle. Taking off with the gear and flaps up will probably require one more engine :-)

Doesn't liners have warning systems for wrong T/O configuration?
Well it depends...

- no flaps, yes A&B have warnings
- too less flaps, don't know the current state of airbus T/O checklists on ECAM but I was flying more than 10 years the bus with T/O ECAM happy with ANY flap setting (1,2 and 3)....

Most of the time T/Os are performed wit F1, but if your calcs were for F2 or even F3 there was NO warning if you put the flap lever to F1 for T/O.....

Another thing is Tflex. Neither on A320 nor on A340 flex temp was asked for in a checklist on my operator. Well, on A300 it was....
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Old 12th Aug 2019, 20:07
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Not familiar with Tflex. Can you give me a quick introduction to this concept? Is the power setting still fixed during T/O (at a lower setting) or will it be changed somewhere along the T/O roll?
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Old 13th Aug 2019, 00:49
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IIRC it was in the mid 70's that I learned that my friend, Col, Carl Crane in Texas had patented a system called Tell Me. It annunciated the distance run during landing or takeoff. I immediately realised that the receiver he was hoping to market was already installed on most aircraft in the form of the Marker and that fan shaped transmissions could be installed on the edge of the runway. Remember, DME was fairly new, and distance on the runway was not generally available. There had been a few accidents in that era associated with landing well off the numbers.

Working out the acceleration was my next leap. It made sense . . . back then. I smelled an investment.

I came back to the UK with an agreement that if he had North America, I could have the rest of the world. I was already in touch with our government's 'development scheme' (or some such) who were soon in possession of my drawings. They paid half of the research and development to successful applicants.

It was only a short time later that I got a letter saying they were already funding a similar system, and mine would be in conflict. I called the folk doing the testing and a nice guy told me their hopes and woes. It seems a BAC 1-11 was charging up and down a runway with doppler looking at the runway surface. A secondary dial on the ASI showed the accelerative progress. It worked . . . sometimes, the doppler unlocking with tedious regularity. Given how quickly DME became available on the runway, I guess it's a good thing neither of us poured too much into our respective dreams.

It had been a subject close to my heart. Despite having passed my performance A in 25 minutes, I was very aware that so much of it was utter bo-lox. Quite meaningless in many situations. For me, the most memorable was Split, with my boss doing the takeoff with a well loaded BAC 1-11. I still remember the thundering of the undercarriage on the uneven concrete slabs. It was soaking up energy. The simpleton on my left said nothing, then or later, despite me having called V1 as we passed over the rocky coastline.

I put a lot of effort into getting the subject discussed and talked it over with a couple of big name electronics manufacturers. There was a lot of interest, but even more inertia. No, the pun has not gone unnoticed.

I expect my phone could do a fair job of it these days.
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Old 13th Aug 2019, 00:55
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Originally Posted by gearlever View Post
Well it depends...

- no flaps, yes A&B have warnings
- too less flaps, don't know the current state of airbus T/O checklists on ECAM but I was flying more than 10 years the bus with T/O ECAM happy with ANY flap setting (1,2 and 3)....

Most of the time T/Os are performed wit F1, but if your calcs were for F2 or even F3 there was NO warning if you put the flap lever to F1 for T/O.....

Another thing is Tflex. Neither on A320 nor on A340 flex temp was asked for in a checklist on my operator. Well, on A300 it was....
I'm guilty of doing that. Fifi caught me. Thankfully
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Old 13th Aug 2019, 04:46
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Most of the time T/Os are performed wit F1, but if your calcs were for F2 or even F3 there was NO warning if you put the flap lever to F1 for T/O.....
Another thing is Tflex. Neither on A320 nor on A340 flex temp was asked for in a checklist on my operator. Well, on A300 it was....
Airbus is generally quick to find fixes and both these issues have fixed. Flex temperature is very much a part of the C/L for a long time now. As far as config warning is concerned in conventional A320 it was just an assurance that you are not outside takeoff configuration. Now Airline can opt for new app that will compare the actual configuration with the MCDU entry. Acceleration check in my opinion is not possible when thrust settings vary by as much as 40% nor is it required when everything else is in place. Trend arrow is a good indicator it can even indicate a wind shear.

Last edited by vilas; 13th Aug 2019 at 05:06.
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Old 13th Aug 2019, 09:55
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Originally Posted by F-16GUY View Post
Not familiar with Tflex. Can you give me a quick introduction to this concept? Is the power setting still fixed during T/O (at a lower setting) or will it be changed somewhere along the T/O roll?
Tflex or assumed temperature method is a smart and safe way to reduce engine wear, increase lifetime.
Thrust will be constant besides physical effects of increasing airspeed on jet engines.

Flex temp
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Old 13th Aug 2019, 13:29
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F-16 re FLEX Temp / AST method. A fictitious temperature is fed to ECU so that a reduced thurst is provided by the engine. This reduced thrust level is pre-calculated to provide exactly the amount of remaining thrust needed for the EFATO - Go case.

For the purpose of this thread, the HOW (Temp) is not relevant, also the De-Rate feature could be used (same goal). The WHAT is - for every takeoff a different thrust is used and thus a reference acceleration pattern is hard to define.
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Old 13th Aug 2019, 15:23
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Originally Posted by FlightDetent View Post
F-16 re FLEX Temp / AST method. A fictitious temperature is fed to ECU so that a reduced thurst is provided by the engine. This reduced thrust level is pre-calculated to provide exactly the amount of remaining thrust needed for the EFATO - Go case.

For the purpose of this thread, the HOW (Temp) is not relevant, also the De-Rate feature could be used (same goal). The WHAT is - for every takeoff a different thrust is used and thus a reference acceleration pattern is hard to define.
Originally Posted by vilas View Post
Airbus is generally quick to find fixes and both these issues have fixed. Flex temperature is very much a part of the C/L for a long time now. As far as config warning is concerned in conventional A320 it was just an assurance that you are not outside takeoff configuration. Now Airline can opt for new app that will compare the actual configuration with the MCDU entry. Acceleration check in my opinion is not possible when thrust settings vary by as much as 40% nor is it required when everything else is in place. Trend arrow is a good indicator it can even indicate a wind shear.
I am going to disagree a little with some of that. Using FLEX/De-Rate will give you closer acceleration for different weights, (for the same aircraft on the same runway length), than using TOGA for every take-off regardless of actual weight. (very light A320 with a very high FLEX temp accelerates similar to heavy A320 with low FLEX, very light A320 with TOGA accelerates much faster than very heavy A320 with TOGA.)
Not suggesting an acceleration check would work.
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Old 13th Aug 2019, 15:30
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I think there is enough to monitor during take-off and no need to add anymore Ďmade-upí acceleration check. Anyway, what happens when rvr 125m?

If both pilots check the the performance data and the numbers are cross checked when inserted into whatever electronic box the aircraft has, then good to go. Gross error check is also useful too.
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Old 13th Aug 2019, 16:05
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With knowledge of V2 speed and runway length combined with aircraft position, you could do calculate somewhat of a minimum of acceleration required.
If that goes below the required acceleration between 40 and 80 knots (groundspeed acceleration, this system isn't for wind shear), give a warning which should produce an abort.

Even with a wrong gross weight and somewhat lower V2 input, the system would likely still catch cases where planes rotate with all engines operating scrape the approach lights.

You could get even more tricky and infer gross weight from actual acceleration given a certain EPR.
That gross weight gives you an V2 to use for the computations.
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Old 13th Aug 2019, 16:26
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Back in my early 737 days we used assumed temperature with paper charts. Later on we got computers which then allowed us to calculate assumed plus derate and thus on short flights allowing even greater reduction in thrust. I remember the first time I used this on a 4000 meter runway being asked by the tower if we had had an engine failure, the difference was that great! The calculation was correct and the tower got used to our high idle takeoffs. Personally I was very sceptical about what the local population thought of this improvement with us thundering over their heads much lower and our noise abatement then adding thrust. An earlier chief pilot in my opinion quite rightly disagreed with this but later on we would see increased thrust at a lot of places at 1000 feet.
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