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If the takeoff weight is underestimated, rotation will be done too early and may result in a case of tail strike.

One example of such mistake is a 747-400 (F-HLOV) in 2006 (case 8 in this study). The crew entered ZFW for TOW (100 tons lower), VR was underestimated by 32 kts.

Boeing documentation mentions every aircraft can be subject to tail strike, at different degrees. Airbus documentation for tail strike prevention doesn't mention any specific protection from FBW.

747 Taking Off (source: The Aviation Herald.)
UA B744 tail strike on Sydney takeoff (photo may not be the actual May 7th 2010 T/O).

  1. I wonder why such basic mistake may be done. Weight could be sensed in some way by the instrumentation, and crew entered values should be challenged if really different.

  2. To prevent the crew from being forced (or tempted) to rotate the aircraft beyond the maximum safe angle, isn't that possible to monitor the T/O progress and in case of low performances alert the crew, and provide an opportunity to reject the T/O.

  3. Airbus FWB embeds many security systems (compared to Boeing), this is surprising that they cannot prevent such T/O tail strikes. I'm sure there are good reasons, just asking to understand the difficulty.


Edit: Based on the answer from Marky Mark, who references the EK407 case, I checked a study published in the aftermath of EK407 tail strike: Take-off performance calculation and entry errors: A global perspective and noted this recommendation for 'TOPMS':

While the above recommendation does not preclude data entry and calculation errors relating to take-off performance parameters from occurring, Transport Canada (Department of Transport) agreed that a take-off performance monitoring system(s) (TOPMS) would provide a significant safety benefit. However, before regulatory authorities establish a requirement for the fitment of TOPMS, a certified system would need to be developed (Transport Canada, 2010).

Basically, a TOPMS, which assists pilots in determining whether to continue or reject the takeoff, can be defined as (Brown & Abbasi, 2009, p. 7).

Are TOPMS now in place?

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    $\begingroup$ I won't post this as an answer because I don't have time to elaborate: but essentially it's possible. Remember though that in the case you mentioned, the crew misjudged the weight: if the aircraft was working off the same data, it would make the same mistake. We could add the ability for the aircraft to weigh itself, but that wouldn't need to be part of the fly by wire, it would also have solved the problem in the example mentioned. Essentially it adds weight and cost for something which could be handled by better procedures. $\endgroup$ – Jon Story Feb 15 '15 at 1:09
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    $\begingroup$ Adding to Jons answer, fly by wire sure is a great thing, but the more you automate it the less control the pilots really have over the airplane. Imagine yourself in a car where you are about to crash into another car and want to leave the lane to go into the ditch, but your car won't let you because it is automated and wants to stay in the lane... Me as I pilot would like to make the decisions in an airplane, and (though I can't think of am example but also generally speaking) maybe sometimes you'd prefer a tailstrike rather them going trough the fence at the end of the runway... $\endgroup$ – Maverick283 Feb 20 '15 at 8:10
  • $\begingroup$ @Maverick283: Agreed, though there is an alternative to all-manual and all-automated, as stated in the TOPMS quote (assist pilots in determining whether to continue or reject the takeoff) $\endgroup$ – mins Feb 20 '15 at 8:27
  • $\begingroup$ @mins Jupp, didn't mean to fight that or anything. While this is mainly about answering your question, there will be others looking this up eventually. I personally find it best to give inputs so that other people get as much out of a question as possible! $\endgroup$ – Maverick283 Feb 20 '15 at 10:27
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    $\begingroup$ There is a simple solution to preventing tail strikes that was employed by the first 747 carrier I flew for. Their takeoff procedure called for an initial rotation to 10 degrees nose up and then holding that attitude until liftoff. The downside of that procedure was that you used more runway than you would have otherwise, and, of course, it depended on the pilot to actually do that. $\endgroup$ – Terry Jan 26 '17 at 21:56
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Boeing has removed the tail skid on the latest B777-300's because they have never had a tail strike and an updated version of FBW will virtually guarantee it going forward. Removing the tailskid saves about 300 lbs.

More info:

Aviation Week Article

Boeing has also decided to remove the tail skid from the 777-300ER as a weight and drag reduction improvement after developing new flight control software to protect the tail during abused takeoffs and landings. “We redesigned the flight control system to enable pilots to fly like normal and give them full elevator authority, so they can control the tail down to the ground without touching it. The system precludes the aircraft from contacting the tail,” Schneider says. Although Boeing originally developed the baseline electronic tail skid feature to prevent this from occurring on the -300ER, the “old system allowed contact, and to be able to handle those loads we had a lot of structure in the airplane to transfer them through the tailskid up through the aft body into the fuselage,” he adds. “So there are hundreds of pounds in the structure, and to be able to take all that out with the enhanced tail strike-protection system is a nice improvement.”

The change was implemented on the line in November and will be offered as a retrofit through a service bulletin. “With a retrofit, you can’t save so much weight because the structure is already in the fuselage, but the drag and maintenance savings is still a nice benefit,” says Schneider. “It is also one of things customers are most interested in retrofitting off the aircraft."

Tail Strike Protection (TSP) logic has been incorporated in the 777 FBW since the -300ER became available. It is available on the 777-200LR as well (despite shorter body); I believe all other models also have it now through the PFCs (200ER, F). The newer -300ER aircraft have the TSP logic ENHANCED and with it came the removal of the tail skid, which saves 323 pounds (145kg) of aircraft weight besides maintenance costs (it's a hydraulic actuated skid).

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  • $\begingroup$ You're saying they built over rotation protection into the EGPWS or that 773 pilots are good enough that they never over rotate and have a tail strike? (there's a :) for the 2nd half of that question) $\endgroup$ – FreeMan Jan 24 '17 at 14:33
  • $\begingroup$ It is all in the software. See my edit above. $\endgroup$ – Mike Sowsun Jan 24 '17 at 18:15
  • $\begingroup$ Thanks for the additional info. That really was intended to be a bit of a tongue-in-cheek comment, but your answer is even better now. $\endgroup$ – FreeMan Jan 24 '17 at 18:22
  • $\begingroup$ It is not the pilots. I belive it is an updated FBW. ( not EGPWS as I said earlier) $\endgroup$ – Mike Sowsun Jan 24 '17 at 18:25
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On Airbus aircraft, the guidance law provides attitude protection on take-off which should prevent a tail strike. However, this is not fool-proof and it remains up to the PF to maintain the correct nose-up angle.

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  • $\begingroup$ Thanks for the reference to EK407. Based on ATSB report, it is very similar to Corsair: -100 tons TOW error in FMGS, early rotation. No real protection (e.g. low acceleration alert prior to V1), only the FD cue to achieve T/O profile speed. The good news is the related release of Take-off performance calculation and entry errors: A global perspective, a study of 20-year tail strikes (including F-HLOV). $\endgroup$ – mins Feb 16 '15 at 7:35
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    $\begingroup$ Sorry but there is a mistake in Marky Mark's answer. The Airbus does possess an attitude protection but it doesn't protect against overrotation. If you are doing a standard flaps 1 takeoff, the protection steps in at 30 degree nose up pitch(!). As stated in the 320 typerating website link, the normal rotation rate of 3 degrees per second needs to be adhered to! In other words, the protection is(!) fool-proof but is far from active at a takeoff. $\endgroup$ – LRT Mar 16 '15 at 10:48
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In principle, yes. The aircraft would have to be able to measure its weight, which rests on the main gear and front gear when on the ground. Measuring a structural displacement which increases with more weight and decreases with less weight, one could determine the aircraft weight.

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