How Much Runway is Too Much?

20 Oct 17 7 Comments

I have the flu and so I’ve decided that this week, you should write Fear of Landing’s Friday post for me.

This video has caused a lot of discussion on aviation forums and I’d love to know what you think. The video is slow to start as it starts at the stand, so I’ve skipped ahead to the start of the take-off roll at about 01:50 in. If you are reading this on the mailing list, you probably need to click through to see it correctly.

The actual take off is at 02:28 and as you can see, the aircraft definitely did use all the runway.

The video appears to have been taken in July 2017 at Bristol Airport. The aircraft is a 737-800. I can’t see any way of working out which flight or what airport it was headed for.

I found the video posted on PPRuNe (Professional Pilots Rumour Network) where the debate spans twelve pages and is still continuing.

For easy reference, here is a screenshot of the aircraft as it starts to climb.

Here are some choice comments, complete with photographic explanations.

So, someone with a smartphone filming from a passenger window is suddenly an expert on aircraft take-off techniques? There is another one on the same site, taken filming towards the tail. And there was me thinking a little knowledge, experience and examinations were needed. Silly me.

 

Just looking at the timer, it looks to me like a normal take-off. When the take-off lasts more than a minute is the time to get nervous!

 

I’m sorry but that does NOT look like a normal take-off. Normally one would expect rotation to occur at the latest inside the markings at the far end, but be firmly in the air by the 1000ft to go point. I have rarely witnessed anything tighter than that in the developed world! That was certainly not the case here.

 

I just showed it to my 7 year old. He knows that it was [expletive deleted] close.

 

Hard to tell, but that looks textbook to me!

In general any delay at Vr and or slightly slow rotation rate on the -800 , and you end up with V2 plus 15 to 25 kts.

In the N-1 case after V1 but before Vr obviously this RWY is tight, and a prompt rotation at Vr and a steady V2 climb is essential.

I was out of there with a full aircraft , over 4 hrs flight and flaps 25 the other day. No margin except for bleeds off next. Worked like a charm!

The Old Lady will perform! Just make sure you do not let her down if Murphy pulls a trick around V1 and the next few seconds…

 

It’s a runway 27 departure, MLG couldn’t have been that far off the ground on the piano keys, if not still on it.

Refer to this picture and tell me how much room for error there is.

If you look at the wing shadow and the background landscape forward of the wing, it is clear the aircraft is rotating at the 1000ft markers and certainly airborne at the 500ft mark.
Depends on what you call ‘tight’.

 

Clearly you haven’t had a chance to see the memo O’Leary sent out to crews.

‘We’ve realised that we’re paying for the whole runway, so use the f*cking thing’

(PS Daily mail this is a joke)

 

“…it is clear the aircraft is rotating at the 1000ft markers and certainly airborne at the 500ft mark.”
Agreed, indeed probably before then..hard to tell because of the image quality but if you use the leading edge wing route/runway edge sightline as datum it looks to me as if rotation has started by at least 1500′ to go i.e. looks like there’s evidence of pitching as they cross the TDZ marker 500′ in/downwind from the main TDZ marking at the upwind end of the runway.

Whether the rotation was slow or not is up to the 737 guys to judge but I’m not sure we can judge off that video. As for height over the runway end.. we all know about possible lenses and forshortening etc, surely that has to be a don’t know?…….

 

I believe that the Boeing training manual states that with both engines operating and a normal take off performed the aircraft should be at a minimum height of 150′ above the runway end. Check “Go/Stop decision near V1”.

 

I’ll reserve judgment due to lack of facts about the takeoff performance calculation, but the above is true. The photo is referenced ground markings and they do not lie. The numbers might well have been correct, but the rotation technique not. If PF was fixated on the runway, and also PM, who then forgot to call “V1” or “Rotate” it could be that no-one was looking the ASI. PF saw the runway end closer than ideal, glanced inside, said WTF and rotated. It was not a ‘haul off’ the runway, but still a normal rotation suggesting no panic. But the CVR would have been interesting in those few seconds, and perhaps during a discussion once in crz.

 

I have been told by finance guys that one of the largest costs involved with the operation of modern airframes is engine maintenance (which can exceed the hull value over its life). The frequency and expense of this correlates very well with thrust/EGT margins on takeoff, so unsurprisingly there is pressure from above to get the job done with the minimum thrust required to meet the regulations.

The performance people have had to get quite creative: we now have AT derates, fixed derates, improved climb, CofG adjustments, packs off, etc. sometimes all used at the same time.
I have noticed over the last few years the end of the runway becoming slightly more prominent on occasions as some of these measures have taken effect but as we are still meeting or exceeding the same requirements as before, it’s more a perception issue than one of safety.

Going back to the video in question, without the FDR and a whole load of other data, I couldn’t definitively say that something was grossly wrong with it. A marginally late rotate call followed by a slightly slower rotation rate would produce the effects noticed on the recording, with the correct thrust setting. If they’d carried on at treetop height for the next couple of miles, then yes but that didn’t happen.

 

If you want to maximize the payload for a given day and runway there is no need for more runway ahead since you are already committed at an earlier point to go. Clearly there are issues with margin and assuming a proper technique and as always other assumptions in play, it’s at least from a performance standpoint I don’t see an issue not using the whole runway for the run if needed.

 

For the non-pilots reading this, Clearway and stopway are two different things.

A stopway is an area beyond the designated runway available as extra stopping distance. It may be surfaced with an energy absorbant material. This is clearly inside the airport boundary with no obstructions. Bristol does not have a stopway.

A clearway is a fan shaped area beyond the runway with no obstructions above the minimal angle of climb. Runway 27 at Bristol has no obstructions beyond the ILS antennas because the ground falls away so if you can clear the ILS you are away free. Other airfields will often have buildings, trees etc obstructing the approach and climb out paths to consider.

 

I downloaded the video, used SMPlayer to split the interesting bits into single frame images, and picked those frames where runway markers were visible, judging the plane’s position by the shadow of its wing. This method is somewhat inaccurate because somewhere in the chain some duplicate frames were inserted (possible to change the frame rate from 25 fps to 30 fps) and the shadow moves as the wings lift up, so when I state that the plane had 40kt at the threshold marker, 125kt at the center of the runway and 150kt over the aiming point, those values are probably fairly close to the truth (maybe +/-2kt?), but ultimately useless.

However, I then cut out images of the 8ft tall winglet in those positions where the wing was over a runway marker (two images for each set of “piano keys”) and aligned them at the runway edge. This makes it easy to see where the plane rotated and lifted off: 450m (1500ft) from the end of the runway, rotating at approx. 1° per second.

Small print: 0s is at 1:57 in the video, as the back edge of the wing’s shadow aligns with the back edge of the “piano keys” (this position is 0m). Pictures 3-12 have the same positional relation to each touchdown marker. The runway image was taken from Google maps and provided me with the positions of the runway markers, assuming those were painted in multiples of 5m.

You’ll need to click on that image above to see it at full-size.

Not to be outdone, a further poster has focused on what can be determined from the shadow of the wing as they travel along the runway.

Despite comments in this thread to the contrary, meaningful metrics can be collected from cell phone video.

In this case, I am looking at the shadow of the wing to judge the relative position of the 737 at it crosses runway landmarks.

Here’s is what I note:
2:11 Early edge of taxiway H. About 1475 meters of runway remaining.
2:21.5: Middle of retired taxiway. About 780 meters of runway remaining.
2:27: End of bar at outside edge of runway. About 356 meters of runway remaining.

So, in that last stretch, the 737 crossed 424 meters in 5.5 seconds. Averaging 77 meters per second or 150 knots.

That’s averaging roughly 150 knots.
At that point, he still had 350 feet on runway in front of the wing – but did not rotate for another second.

So as best I can tell, this was a delayed rotation.

So, now that you’ve had all the in-depth armchair analysis (there’s more on the PPRuNe thread if you wish to look, including detailed discussions on trigonometry and performance values and the position of the sun at the time of departure!), tell me what you think!

In your opinion:

  • Is this a normal take-off with sensible use of the runway at hand?

  • Did something go wrong?

  • Is it ludicrous to try to work it out from a phone video taken from the back?

Let me know in the comments! If you are on the mailing list, you need to click through to take part in the discussion! I’m looking forward to seeing your thoughts.

Category: Miscellaneous,

7 Comments

  • For the record: read the comments posted by experts and then ask the question (again): Since when are Joe and Jane Soap experts on the take-off performance of modern jet airliners?

    All factors that determine the take-off are subject to very complicated calculations. If a crew had to so it all “from scratch”, using the graphs and tables in the Flght Manual, they may just get airborne before they run out of duty time. So the crew will use performance tables with pre-calculated data for the aircraft and the runway for take-off.
    Add variables, like payload, fuel weight, air temperature and wind and the crew can determine quickly what the allowable weight will be: number of passengers, limited by the amount (weight) of fuel required.
    When all the variables entered, the crew will then be able to read the V-speeds and whether or not a “flexi-power” setting may be used.
    When Ryanair was a fledgling airline we flew the BAC 1-11 500 into and of course out of Coventry. The “Vee-one” call came well before “Rotate” and by that time the end of the runway was no longer visible from the cockpit.
    We did not use flexi-power, but some take-offs required “wet” power: de-mineralised water would be sprayed into the turbines which gave a very substantial amount of extra power.
    All these factors are carefully calculated.
    The general public should not be taken for serious in this kind of matter. This is nothing but sensation- seeking nonsense.

  • Rudy, to be fair, there were experts – commercial pilots, some of whom who knew the airport well – on both sides of the argument. I think we agree that an analysis from the backseat isn’t particularly trustworthy. But is the video?

    I think the video is not the victim of odd foreshortening or perspective, so it does seem to me that the key question, that is, did the aircraft use all the runway, is very likely to be Yes, even at that angle.

    But I do agree with you that there are so many variables at play, the secondary questions are harder to answer: was this a mistake? And is this an issue?

    It is, of course, a tempest in a teacup, as the aircraft departed safely and landed without incident. Nevertheless, I think it is interesting to ponder.

    Also, I’m feeling better now, thank you for filling in. :)

  • Sylvia,
    The bottom line is that crews WILL use TL tables (also known as RTOW – Regulated Take-off Weight – tables) to give them the information they need.
    In my day they were in the ship’s library, maybe in modern days they can be conjured up electronically, I do’t know. I retired too long ago.
    But the bottom line is that information gleaned from official publications, like elevation, runway, obstacles and intersections in the AIP and performance data from the AFM (including approach- and landing climb requirements) are fed into a computer. The company I worked for got the tables through a Swedish publisher called Flygprestanda, but the publisher is irrelevant.
    We got them for every aircraft, data supplied to the publishers and based on not only type of aircraft but also for individual aircraft, based on weight and balance data provided to them.
    So before take-off the crew can, must and WILL consult the tables. E.g. “Anyville, runway 33L” aircraft type and series already taken into account. Actual take-off weight from the loadsheet. Now check the departure ATIS for actual air temperature and wind and hey, presto: it will be possible to read quickly what the V-speeds will be, the take-off pitch angle, the flap setting (or settings if there is a choice), whether or not an intersection may be used and what the power setting may be, including a flexi-setting if allowed. Some aircraft types, most modern ones insofar as I know, have a “flexi-power” select button.
    Any reasonably well-trained crew will be able to use the tables and derive the data virtually instantly. It is not at all difficult and I never heard of a mistake.
    Insofar as I am aware, an engine failure on take-off will automatically cancel flexible power in aircraft fitted with a “Flexi-power select” button.
    Otherwise, use of flexi power will still meet the performance criteria and can be overridden in an instant.

    So I still feel that all the hullabaloo about this “late, prolonged take-off” can be relegated to the realm of male bovine manure.

    I can (maybe I will) send you a photo that I took in the 1970’s.
    I was flying a PA18 Super Cub on a banner-towing mission on a warm summer’s day in the Netherlands.
    I was no. 2 in a formation and took the photo with a Zeiss Ikon Contaflex with a standard 55 mm lens (on film, of course).
    We were very close together, yet the picture seems to suggest a comfortable distance between the aircraft. At the time, I probably had accumulated more than 2000 flying hours on banner towing missions alone and we could maintain a very tight formation effortlessly.

    But the point I am trying to make is: Lenses ALWAYS have en element of distortion. Look at videos on U-tube of “hairy” crosswind landings. The picture, if taken with a long lens, is ALWAYS compressed.
    And so I believe that a certain element of lens distortion is also present in your post about “How long?”

    How Long is a Chinese? or
    How Long is a Chinese! A subtle difference can change everything!
    With apologies to our Asian friends. My daughter-in-law is Chinese, no insult intended !

    So, Sylvia, this article is interested only as it illustrates once again how people who do not know the difference between a Piper Cub and a 747 think nothing of spouting ccrrraaappp and presenting it as a near-incident on U-Tube !

  • Rudy — the rule that I was quoted (40 years ago in the US) was that the plane had to be able to lose an engine on reaching rotation speed (or maybe takeoff speed) and come to a safe stop (on the runway IIRC rather than any stop zone) with brakes and the remaining engine(s). Was that incorrect? If not what would have happened if they’d lost an engine — could they have stopped in 1500′ from a plausible speed? Or do you think that rotation actually happened further than 1500′ from the end of the runway, or that the pilot simply failed to rotate at exactly the right point?

  • PF: “Bit close, what? I’ve told O’Leary we need to change our takeoff procedure.”

    PM: “Word fam. Some day the passengers are not going to scream like that and we won’t know when to rotate at all.”

  • Chip — I’m not Rudy, but perhaps I can help.

    The speed at which the aircraft is assumed to lose an engine for purposes of certification is called VEF. To come to a safe stop, the pilot must take the first abortive action at a speed no greater than V1, which is slightly after VEF to allow for the pilot’s reaction time. In any case, both occur significantly before VR, the aircraft’s rotation speed. Once the aircraft accelerates past V1 the pilot can no longer abort and is committed to the takeoff.

  • “Use of the runway”, by certification regulations, requires that the aircraft lifts off such that the runway ends no sooner than halfway between liftoff and screen height (35′, the aircraft should be at climbing speed then); and for take-offs with 4 working engines, a 15% safety margin is added to the take-off run on top of that. The flight on the video met the first criterium but not the 15% safety margin, possibly due to the rather slow rate of rotation of about 1° per second (normally 2-3° per second).

    This take-off was not normal, but safety margins ensured it was uneventful. Since these facts were worked out from analysing the video, obviously I don’t think it is at all ludicrous, though it does require rather more work to extract solid data from it.

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