Unreliable airspeed above V1 on B744

[SRS]

Our FCTM states that in case of suspected unreliable airspeed indication rotate to 15*with full thrust , gear up, continue until acceleration altitude. Then memory items and pitch 10* power 90% to MSA. At that time troubleshooting can begin. The problem here is what is the acceleration altitude? Boeing does not commit itself, unlike Airbus that state it as 1500 feet. FAA minimum for any failure is 400 feet. I have worked with airlines that used 800, 1000 and 1500 for engine failures.

Any ideas or experiences would be welcome.

thanks

[john_tullamarine]

You should have SOP protocols for your operation. Unreliable airspeed should not change the departure procedure, only the means by which you keep somewhere near the required IAS.

[Three Wire]

On the B777, funnily enough, the acceleration altitude was embedded in the FMS. It was also discussed in the FCTM somewhere.

[FullWings]

Logically, the AA is the one you are using on the day that takes into account your location and the ambient conditions? Why would you change it?

Subtle difference on the 777 is that we maintain the thrust we set for takeoff and 15degs up to AA. I suppose that’s two engines vs. four engines and the margins thereof.

[mustafagander]

As I recall it if the ASI goes nuts you can do a quick circuit using GPS G/S to keep speed within the ball park and land.
Forget troubleshooting, get back on Terra Firma and write it up.
I agree with SRS when handling the initial leaving the ground but roll into a circuit and land SASPO.

[FullWings]

Although that is an alternative to have in reserve, should circumstances require it, you are leaving quite a lot in the hands of fate as well as ignoring basic QRH drills.

Once recognised, UAS is relatively straightforward to deal with in the proscribed manner and once under control, allows things like landing performance, fuel dumping, approach planning and other minor details to be considered. There is also the chance that in running the checklists you might manage to identify some correct indications and change air data sources, such that you can continue the flight. Another factor is that UAS can be quite subtle, so it takes a while to recognise; at that point you could be a long way from where you thought you were, so current groundspeed, attitude, etc. are not good datums to base a recovery on.

“Roll into a circuit and land” is very rarely an optimal solution to most problems encountered in modern commercial aviation. If there’s a fire inside your aeroplane that won’t go out, sure, but for pretty much everything else, getting away from the ground and having a good think/discussion about how/when to get back onto it is the safest course of action.

[john_tullamarine]

You can handle IAS problems without too much concern so long as you keep your cool and have a good knowledge of pitch and thrust settings for configuration. One of my standard exercises in endorsement training was to work the student up to the point where he/she could handle a single pilot, low vis takeoff with a pitot static failure, run the circuit and land off a low vis (the better student would be challenged with a 0/0 situation) ILS. Great for stick and rudder confidence building.