Static takeoff at higher weights.

[JammedStab]

Does anybody out there have a company requirement to do a static takeoff at higher weights?

I just read this in an old accident report...."It is known that some operators prohibit rolling take-offs on some runways If the take-off weight is within 10,000 kg, (in the case of the B747), of the maximum permissible for the particular conditions prevailing, and there would seem to be some merit in
this practice.

[john_tullamarine]

Can't see much concern at near gross .. empty, on the other hand, gives a measurable difference in the early acceleration. Match the latter with a minimum length runway and things could get a tad sweaty.

[JammedStab]

Can't see much concern at near gross .. empty, on the other hand, gives a measurable difference in the early acceleration. Match the latter with a minimum length runway and things could get a tad sweaty.

I would have thought it would be more of a concern near gross. I am assuming that the intent of the accident investigators is the concern about wasted runway when doing a rolling takeoff or perhaps more specifically that some pilots might waste more runway than others depending on the rolling takeoff technique used.

Concerning rolling takeoffs, the report stated "However it is clearly less precise, and if the aircraft needs to turn through a large angle at slow
speed, possibly using asymmetric thrust, is then allowed to move slowly forward while thrust levels are balanced and then throttles advanced, valuable runway distance can be used before take-off power is established."

[john_tullamarine]

Generally it is presumed that a rolling start from the taxy will provide an acceptable outcome.

For acceleration from static,

(a) the low weight case is more of a concern as the breakaway thrust required is lower .. ie the aircraft will be expected to have travelled some distance prior to finally having the thrust set correctly.

(b) for weights approaching gross, the breakaway thrust is higher and, for the same time allowance to set thrust, the aircraft will have travelled a shorter distance .. in my experience, prompt pilot action sees takeoff thrust set in the first few feet of travel at heavy weights.

Re the specific comments .. pilot technique has to be prompt without needless dilly dallying .. spin up and then push the levers up (or use the button) .. should only take a couple of seconds. A pilot who takes a long time really needs some corrective training, methinks.

Rolling takeoff should not be a problem .. as the aircraft approaches the runway heading, the engines go to spin up and then to the required takeoff setting. I can't recall any problems on the line for the 727/737 .. perhaps it is different on other Types ?

[mustangsally]

Several decades ago, back when using line charts and graphs, the company added 500 feet to the static takeoff roll. If the result was equal to greater than the runway available a static takeoff was required.


The older jet engines were also slower to accelerate particularly in the lower RPM ranges. Some engines were first set at a mid-range power setting prior to brake release. Some of the older large fan engines even set takeoff thrust and cooked the engine for 30 seconds prior to brake release.


Todays engines with variable stators have greatly improve throttle response, thank goodness.

[742]

From the Boeing Flight Crew Training Manual for the 747 (emphasis added):


"A rolling takeoff procedure is recommended for setting takeoff thrust. It expedites the takeoff and reduces the risk of foreign object damage or engine surge/stall due to a tailwind or crosswind. Flight test and analysis prove that the change in takeoff roll distance due to the rolling takeoff procedure is negligible when compared to a standing takeoff."


I am inclined to take this at face value since both Boeing and Airbus will do pretty much anything to gain a few kilos of payload.

[john_tullamarine]

If the result was equal to greater than the runway available a static takeoff was required

A matter for corporate risk assessment.

However, I consider that

(a) a reasonable view, provided the concern is restricted to ASD considerations, when considering standing start on the brakes compared to progressive thrust application. Otherwise it is an excessive conservatism for the majority of situations.

(b) but not for a rolling on start where the aircraft is moving along at a clip and the thrust setting is prompt. Typically, this is the case for a 90 degree roll on where the turn is continued into the takeoff without stopping and the spin up occurs in the latter part of the turn .. ie the final thrust increase occurs as the turn is completed and there is no dilly dallying trying to get lined up on the centreline prior to thrust setting

Some engines were first set at a mid-range power setting prior to brake release

For a rolling start this is the aim .. we want the final thrust acceleration to be in the higher acceleration range. Keep in mind a rolling start does not include a progressive thrust setting from a stationary start. Chalk and cheese, although, for near gross weights the difference brakes on/off is pretty trivial.

[stilton]

Not the most scientific conclusion but I always thought you would minimize runway use by a rolling start with engines spooled during the last stages of the line up then immediate setting of t/o power once aligned (I think this is what JT is describing)


The big advantage to me is you have take off power set at almost the exact same spot as a static procedure but you keep your momentum, starting off with at least 10-15 knots.


As long as you don't waste runway with your line up technique !

[john_tullamarine]

.. that's the story ...

[JammedStab]

As long as you don't waste runway with your line up technique !

I think this is the concern.

Some aircraft should be fairly straight prior to adding thrust for takeoff as a TO warning will sound if the body gear has not straightened. Therefore more room may be used for line up as compared to some of the narrow body aircraft that had the thrust levers stood up while still 30 degrees from runway heading.

[john_tullamarine]

a TO warning will sound if the body gear has not straightened

I presume that this does not make any difference to the starting point for either technique ? ie not overly relevant to the discussion I wouldn't have thought.

[Intruder]

Since one of the major reasons for the rolling takeoff is to reduce the probability of FOD ingestion at high N1 and low airspeed (~<30 kt), I would think it even more important at high TOGW, with the higher N1 and slower airplane acceleration.

Indeed, the 747 body gear centering has little or no bearing on the subject, since the airplane has to be aligned on the runway regardless of other takeoff technique. In general, throttles are not brought above 40% N1 (normal max thrust for taxi) until hands are off the tillers.

[JammedStab]

Thanks for the input John.

As for the original question of whether anybody is following the recommended technique, based on the number of affirmative answers received, it appears few are.

I guess the only thing I am left with is this accident report to a 747 in Hong Kong on a field limited takeoff.

http://ebook.lib.hku.hk/HKG/B35835126.pdf

Makes an interesting read.

[Amadis of Gaul]

If the only thing you found to support your concerns is a 32-year-old report...

[JammedStab]

Instead of telling us how old the report is.....how about some of your expertise on why you might disagree with the report. The report may be wrong but how about sharing your knowledge of why you are insinuating this.

I don't expect any useful reply of course as you have basically just given us an opinion that accident reports in general are no longer valid after a certain time period.

[No Fly Zone]

Come on now... At least try to be nice. Even to poorly informed poop ;)heads.

[JammedStab]

After searching the internet, this is the only aircraft I have so far found that makes allowance for it. It would appear that this manufacturer is one of few if any others to feel that it is of importance. They however appear to do it for all weights not just the heavyweights as suggested by the accident report.

ROLLING TAKEOFF RUNWAY LENGTH CORRECTION
Reference: Excel AFM TC 56XFM-TC-R12-08
XLS AFM Page 3-97

TAKEOFF

STATIC TAKEOFF
1. Throttles – TO DETENT, Check TO N1’s.
2. Engine Instruments – CHECK NORMAL (no dashes, FAIL messages, or incorrect
indications).
3. Brakes – RELEASE.

ROLLING TAKEOFF
1. Computed Takeoff Distance – ADD 500 FEET.
2. Brakes – RELEASE.
3. Throttles – TO DETENT within 500 feet after brake release, Check TO N1’s.
4. Engine Instruments – CHECK NORMAL (no dashes, FAIL messages, or incorrect indications).

[Amadis of Gaul]

It's not that the report is necessarily invalid. It's more that the underlying "concern" doesn't seem particularly valid since even someone as thorough as you, JS, only managed to find one accident where it could be described as a factor.

[JammedStab]

One accident report and one AFM that takes it into account. However, there are thousands of accident reports that I have not read and many AFM's that I have not read.

Once again using your logic, if there is only one accident report on the subject, it does not appear to be a concern.

There are many well known accidents where there is only that report about the particular factor causing it. Pt2 probe icing on Air Florida in Washington, United DC-10 loss of all hydraulics due to engine explosion, faulty bulkhead repair on JAL 747 blowing the tail off, Engine falls off DC-10 in Chicago leading to slat retraction.

All these were causes for concern.

I was hoping that you might explain why the authors of this report should not be concerned. Simply because no one else ever had been before?

Actually, the original question was simply whether anyone else was taking the issue into account. It appears that some Citation operators are.

Thanks

[JammedStab]

EMBRAER EMB-120
PW-118B
INTRODUCTION

13. Rolling Takeoff Corrections

If the takeoff is to be accomplished utilizing a rolling takeoff, a weight penalty must be applied to the runway limit weight. Subtract the figure shown (ROLL T/O-LBS or ROLL T/O-KGS) from the zero wind runway limit weight after considering temperature and wind as described above. The resultant figure is the maximum runway limit weight with a Rolling Takeoff.

[john_tullamarine]

I suspect such considerations relate to initiating a rolling start from a standstill .. does the AFM provide that caveat ?

[Amadis of Gaul]

I suspect those considerations for Citation Excel and Brakillia operations have little relevance to Jammed Stab's 744...

[john_tullamarine]

On the contrary .. much the same in principle .. only the numbers are different.

[Intruder]

...but Boeing sez it just doesn't matter for the 744...

[JammedStab]

On the contrary .. much the same in principle .. only the numbers are different.

Thanks John. In response to your earlier question, I can't tell you any more detail as this was copy and paste from internet searches that only found excerpts from the associated AFM.

...but Boeing sez it just doesn't matter for the 744...

Correct. And the same for the 737 and 727. Actually, in the report Boeing did give the investigators(for 747-200) some performance information showing a small penalty.

Someone posted this about Embraer jets in an earlier PPrune discussion on the subject...

"Normal Takeoff up to 10 kt tailwind: Pilot lines up the airplane on the runway, applies brakes and adjusts thrust to 40% N1, when engines stabilize at 40% N1, releases brakes and advances thrust levers to TOGA detent.
NOTE: For normal takeoff with tailwind up to 10 kt, performance data is valid from the point where takeoff thrust (N1 target) is achieved.
Normal Takeoff with tailwind above 10 kt (If allowed by AFM):
Refer to TAIL WIND TAKEOFF of this section.

Static Takeoff: Pilot lines up the airplane on the runway, applies brakes, adjusts thrust to 40% N1, when engines stabilize at 40% N1, advances thrust levers to TOGA detent. Release the brakes when the takeoff thrust (N1 target) is achieved.
NOTE: Due to the possibility of compressor stall, a static takeoff is not recommended with a crosswind greater than 25 kt.

Rolling Takeoff: Pilot lines up the airplane with the centerline and, if cleared for takeoff, adjusts thrust Levers to 40% N1 without applying the brakes. When engines stabilize at 40% N1, pilot moves thrust levers to TOGA detent.
NOTE: For rolling takeoffs, performance data is valid from the point where takeoff thrust (N1 target) is achieved. "

I guess the bottom line is that some manufacturers consider it and some(perhaps most) don't. And not many airlines take any extra precaution at heavy weights.

[JammedStab]

Now I know that some feel that a Citation Excel and Brasilia have little relevance to a 744(although John Tullamarine has corrected that notion), for those that relate only to size, I did find this interesting statement...

"In the C-5, we took a 250 foot "line-up" penalty and a 750 foot penalty for rolling take-offs, i.e. the assumption was 250 feet to line-up off the taxyway and an additional 750 feet was added for rolling take-offs."http://www.pprune.org/tech-log/240778-rolling-vs-static-takeoffs.html#post2800425