Built-In Bank Angle Limits

[Badmachine]

Do large commercial Boeings have built-in bank angle limits as Airbuses do under autopilot or manual control? (e.g: 25, 35 or more degrees)

Are these built-in limits if any, easliy adjustable or overcome?

In the event of built-in bank angle limits, how does the aircraft or FMC behave if a route contains a turn with a bank angle exceeding such limits?

Thanks.

:ok:

[exeng]

Aural warnings on the 737 etc saying "Bank Angle - Bank Angle"

On more modern Boeings such as the 777 series (and probably the 787 I would imagine) the same aural warning, but in addition the 'aileron feel' effectively doubles in force making it much more difficult to roll in more bank. Haven't flown the 777 for about 10 years now but I think that about sums it up.

In regard to a turn any Boeing will go up to, but not exceed, 30 degrees of bank with the A/P engaged. Should a SID require a tight turn then the pilot should ensure that a speed limit is programmed into the FMC prior to and after the turn, plus he must ensure that the aircraft is actually flown at that reduced speed.

To expand a little: if the FMC is programmed with the correct reduced speed to reduce the radius of turn then with Vnav engaged the A/P will fly the radius of turn calculated by the FMC up to 30 degrees of bank. If the FMC is not programmed with the correct reduced speed then the A/P will fly the FMC calculated radius of turn regardless of speed mode selected (i.e. Vnav not engaged but flying 180 kts one degree of flap say) and so may bust a SID requirement - this is because the A/P will follow the Lnav track calculated by the FMC given the default speed accelerating to 250 kts below FL 100. Also if the FMC is actually programmed with the correct reduced speed but the pilot elects to use a higher speed in a mode other than Vnav then again the A/P will fly an increased radius of turn because it is limited to 30 degrees of bank.

Time to stop as I am getting very giddy now!

So to sum up: Get the other pilot to programme the FMC, ignore it, and then fly the SID holding flap one until the turn is complete intercepting the radial on raw data.

Hope this is of some help. Note: Life was so easy on the 737-200 as we just flew the SID.


Regards
Exeng

[MarkerInbound]

744 has a BANK LIMIT selector, AUTO, 5, 10, 15, 20 or 25. I've never moved it out of AUTO, which uses TAS , flap position and V2 to figure out what the auto pilot will do.

At least over here, if there needs to be a control on the radius of a turn, it will be done by limiting the aircraft speed and not requiring excessive bank angle.

[Badmachine]

Thanks Exeng and MI. Useful information.

By the way, do the Boeing bank angle limits vary by airline or nation?

Are the limits imposed by FMC software or based on other manual settings?

Thanks.

:ok:

[Denti]

So to sum up: Get the other pilot to programme the FMC, ignore it, and then fly the SID holding flap one until the turn is complete intercepting the radial on raw data.


Allways good fun, but not anymore possible with purely RNAV or even PRNAV based SIDs. Those should have the relevant speed limits coded in though and it is part of the preflight briefing to assure they are.

On the 737 you have a bank angle selector that allows up to 30° of bank, however depending on AFDS mode it can command a bank up to 30° regardless of the selector position. GPWS provides warning callouts, at 32 to 33° a soft "Bank Angle" warning, from 45° on a hard "Bank Angle" warning. That might depend on company pin programming though.

[aterpster]

Denti:
Allways good fun, but not anymore possible with purely RNAV or even PRNAV based SIDs. Those should have the relevant speed limits coded in though and it is part of the preflight briefing to assure they are.

In RNP AR procedures, with all their RF legs, crews are expected to know the normal speed limits. Only less than standard speed limits are charted on the procedure (and, hopefully, in the FMS although we have seen errors already).

With an RF leg if you exceed design bank angle you can reach a point where the "trolly simply departs the tracks."

[bigduke6]

For 747-400....

A/P and FD commands max bank of 25 degrees. Using LNAV, will normally only command 25 if a sharp turn is required on a SID, holding pattern, or at significant dog-leg in the airway at altitude. Most turns at altitude are shallow, less than 15 degrees.

The 'bank angle limit" switch can be takes out of AUTO and as already mentioned, be positioned between 5 and 25 degrees. LNAV will still fly what it wants/calculates, but if using Heading Select, AP or FD will use the limit you have now give it. Somewhat useful in the sim for 1 or 2 engines out to limit the bank angle to 15, if desired. As a note, all engine out turn procedures that I have seen specify a max bank of 15, but this is typically exceeded, and the normal 25 is used.........no one seems to really suggest using bank limit function for some unknown reason. Of course, you can just ignore FD and set your own bank angle........:ok: