Auto mode in HDG SEL bank limit

[Hardy Heinlin]

Wait a minute ... according to my old data that I saved (can't recall the source), the limit is 15° also when TAS is greater than 381 knots.

What's your TAS in your cruise scenario?

I have no plans to remove the TAS criterion from my bank limit logic. Your cruise TAS is probably higher than 381 knots, so you will keep getting your 15° limit in cruise anyway, with and without E/O.

[emerydc8]

Hi Hardy,

My TAS in my situ is 484 knots and, yes, the Atlas material is not in any way contradictory to the assumption that it could be aircraft or company specific. I agree.

Not to mix apples with oranges, but this will support your above epiphany that a 15 degree bank angle limit in HDG SEL auto is a function of TAS: I was lookng at an old 767 manual and happened to notice that with HDG SEL in auto, the bank is limited to 15 degress any time the TAS is above 250 knots. So, I guess the 15 degree bank limit in normal cruise flight is not unusual when compared to other aircraft.  I am pretty sure it will still do 25 degrees of bank if turning in LNAV, but in HDG SEL auto, I can't recall a time that I had to make a turn more than 20 or 30 degrees at that TAS, so I may not have noticed that it was limited to 15 degrees of bank. Interesting.

If you happen to find that 381 knot material, I would be interested in seeing it.

[Hardy Heinlin]

This logic here is used in Precision Simulator since version 1.0.

Quote from the PSX manual, page 138:

Limit is 15° if IAS is below V2+90 with flaps up, or if any engine is inoperative, or if TAS is greater than 381 kt, else: Limit increases 15° to 25° with TAS decreasing 381 to 332 kt. Below 200 ft radio altitude, limit is 8°.


What I want to modify in the next update is the condition "if any engine is inoperative". I think this condition should be restricted to a certain IAS.

[emerydc8]

Very good. I think you have cleared up the issue of bank angle limit at high cruise TAS. Thanks!

[Britjet]

Hi Jon,

A very interesting run-through of the NATS contingency procedure. In BA we did train this, pretty exhaustively.
If I may make a couple of observations..

The NAT "contingency" procedure, as it is called, makes no allowance for an automatic 180-degree turn. That is a common misconception, and has been carried out numerous times in the past without ATC getting too upset about it. Nevertheless, it doesn't exist.

The contingency procedure allows for a 15-mile offset - but traveling in the same direction. The idea, as you say, is to minimise descent during this period, and stabilise at an intermediate 500ft level. Once offset, any further descent or directional change would require ATC clearance unless the pilot deemed otherwise - which he might, but I would rather delay a 180 turn for a minute or two to get ATC clearance rather than hit someone coming the other way on a weather deviation or crossing track :-)

As you say, minimal height loss before you reach the offset is paramount - due to other traffic on the tracks. However the FMC engine-out method that you describe will not achieve that. It is very important to also select "E/O SPD" on the Engine-out cruise page, or the FMC will command a LRC descent - which will be immediate and rapid. You avoided that by using V/S, but there is no need to do so. E/O SPD will give you a much reduced  descent rate in VNAV (it actually flies level for maybe a minute or two in the real jet as the speed bleeds back) and then it will descend at circa 300fpm.

With regard to the return track - as you say it is difficult. Another way to handle a possible situation like this is to insert the reverse track points on route 2 - and execute as required. very neat..

As you say - a difficult manoeuvre.

Peter

[Britjet]

Hardy,

I don't know what the criteria are but the 15 deg limit at high TAS on the 747 certainly has merit. I have seen it in numerous occasions. It is very noticeable.
Interestingly the 777 didn't do that - it used as much as nearly 30 degs bank for even small turns at high altitude- quite alarming - the cabin crew hated it for this reason - lots of G when they were doing meal service, leading to nausea. They initially blamed it on cabin air quality. I know that BA did a lot of research on it and I think they modified the bank criteria with Boeing..


Peter

[emerydc8]

Hi Peter,

You are absolutely right. I tried selecting E/O SPD at 5L before executing and it does descend at roughly 500 FPM. At that altitude and weight, the default LRC DD speed is .858/280 and the E/O SPD is .83/272, so it does give you a bit more time before you have to start down. Also, when you finally do set a lower MCP altitude and start down, it doesn't have a tendency to dive for the speed as it does with the LRC DD.

So, I'll revise my procedure to select VNAV, select ENG OUT, select E/O SPD at 5L (instead of the default LRC DD), set the lower MCP altitude, and then execute. I tried this several times and if you start the 15-degree bank turn just as you execute, it puts you 3 miles away from the track as you pass through FL365, which is very close to what I was getting with V/S, but much better to have some VNAV protection in this scenario.

I hear they plan to go to 1/2 degree (30 mile) spacing on the NAT soon because the carriers are worried that the current scheme will become saturated and they are pressuring the authorities. I have a friend who is one of three nav specialists at the FAA and he issues carriers their B039 NAT/MNPS ops specs. He said he can't believe we haven't had a midair so far; and if I saw the reports that came across his desk I would be blown away -- like certain major carriers doing the whole crossing at the wrong altitude or on the wrong track. I suppose it's just a matter of time, considering the accuracy of the GPS. At least in the old days with the VLF/Omega or the Carousel IV you were off enough that you probably wouldn't hit another aircraft even if you were on the same track and altitude.

Thanks again for the valuable information.

Cheers,
Jon

[emerydc8]

This logic here is used in Precision Simulator since version 1.0.

Quote from the PSX manual, page 138:

Limit is 15° if IAS is below V2+90 with flaps up, or if any engine is inoperative, or if TAS is greater than 381 kt, else: Limit increases 15° to 25° with TAS decreasing 381 to 332 kt. Below 200 ft radio altitude, limit is 8°.


What I want to modify in the next update is the condition "if any engine is inoperative". I think this condition should be restricted to a certain IAS.

Hi Hardy,

I just wanted to clarify two questions about the above-quoted section of the PSX manual with regard to the bank limit selector in auto. When we discussed this issue last year I was more focused on how it affected a 180-degree turn on the NAT.

Turning to a question on takeoff, if you have all engines operating and you did an immediate turn after takeoff at V2 (say you got slow before entering the turn), will it still limit the bank angle to 15 degrees or is this only for an engine out?

Also, on a climbout (say flaps up and climbing through 11,000'), if you are at 332 knots TAS and you lose an engine, will the AFDS command 25 degrees of bank in a turn or does the engine failure still cause the AFDS to limit it to 15 degrees. Just trying to get this straight. Any input here would be appreciated. I presume the change you made was to allow up to 25 degrees of bank with an engine inoperative once reaching V2+10? Thanks.

Jon D.

[Hardy Heinlin]

Hi Jon,

if your questions refer to the real AFDS, I cannot give you definitive answers, unfortunately. It may be airline or FCC version specific. Somebody would have to check it on the real ship or sim ...

Perhaps someone else on the forum has some experience in this special detail?


Regards,

|-|ardy


This is the modification in PSX version 10.0.6:

"0.6.0038. HDG SEL auto bank limit: E/O related 15° limit condition is now disabled above V2+10."

[Britjet]

My experience (BA Sim) is that the bank is not limited by an engine-out situation once you have exceeded V2+10.
The FD is quite happy to wind you round turns (including ILS intercept) at bank angles up to 25 degs (and even more, if I recall correctly - but I can't recall specific examples).

Peter

[emerydc8]

Thanks, Hardy. I think you were correct to make the change and glad you did. The bank should not be limited to 15 degrees with an engine out once past V2+10. This is also consistent with the Boeing FCTM.

Peter, can you give your thoughts on my first question, where you do an immediate turn after takeoff with all engines operating? If you are at V2, will the auto position limit the bank to 15 degrees? I guess a better way to ask this is, will the auto position limit the bank to 15 degrees between V2 and V2 +10 regardless of whether you have an engine out.

The latest FCTM (Rev. 5 June 2015), leaves me wondering if there is a difference between an immediate-turn-after-takeoff on all engines versus three engines. The E/O refers to the AFDS limiting the bank, but the all-engines does not, even though both state that bank angles up to 25 degrees are permitted at V2 +10. I realize that climbing out at V2 on all engines is abnormal and I honestly don't know whether the AFDS would limit the bank to 15 degrees in this situation because I've never tried it; but I am curious whether it would.

Immediate Turn after Takeoff - All Engines
Obstacle clearance, noise abatement, or departure procedures may require an immediate turn after takeoff. Initiate the turn at the appropriate altitude (normally at least 400 feet AGL) and maintain V2 + 10 to V2 + 25 knots with takeoff flaps.
Note: A maximum bank angle of 25° is permitted at V2 + 10 knots with takeoff flaps.

Immediate Turn after Takeoff - One Engine Inoperative
Obstacle clearance or departure procedures may require a special engine out departure procedure. If an immediate turn is required, initiate the turn at the appropriate altitude (normally at least 400 feet AGL). Maintain V2 to V2 + 10 knots with takeoff flaps while maneuvering.
Note: The AFDS limits the bank angle to 15° until V2 + 10 knots to maintain at least adequate maneuver margin when LNAV or HDG SEL is engaged and the bank limit is in AUTO. Bank angles up to 25° are permitted at V2 + 10 knots with takeoff flaps.

Thanks.
Jon D.

[Hardy Heinlin]

I say the limit is 15° also if the IAS is below V2+90 with flaps up -- this agrees with all these texts (they refer to takeoff flaps, not to flaps up).

[emerydc8]

Is the V2 +90 a compromise between a light takeoff and a takeoff with weight above 680,000lbs (309,000k)?

747-400
During flap retraction, selection of the next flap position is initiated when reaching the maneuver speed for the next flap position. The flap retraction schedule for the 747 differs from other Boeing models because the flaps are not retracted until the maneuver speed for the next flap position is reached. For example, flaps 5 is
selected after reaching flaps 5 maneuver speed. During flap retraction, full maneuver capability or at least 40° of bank (25° of bank and 15° overshoot) to stick shaker is provided while retracting the flaps through flaps 1. At 680,000 lbs (309,000 kgs) and below, full maneuver capability exists with flaps up and at flaps up maneuver speed (VREF 30 + 80 knots). However, above 680,000 lbs (309,000 kgs) full maneuver capability does not exist until reaching VREF 30 + 100 knots. For this reason, limit bank angle to 15° with flaps up until reaching VREF 30 + 100 knots.

I can tell you from my own experience that the AFDS will limit the bank to 15 degrees until VREF 30 + 100 on a takeoff above 680,000 with all engines operating.

[Britjet]

You are referring to flaps up, Jon, I take it?
Peter

- and with regard to your low speed low altitude turn, I think so, although it is very difficult to prove!

[emerydc8]

You are referring to flaps up, Jon, I take it?
Peter

- and with regard to your low speed low altitude turn, I think so, although it is very difficult to prove!

Yes, bank angle is limited to 15 with flaps up until VREF30 +100 (for takeoff weights above 680,000 lbs). The older AFDS would allow up to 25 degrees of bank after reaching VREF30 +80, but the logic was later changed to VREF30 + 100 for heavier weights. From the FCTM:

747-400
Note: On some earlier FCCs, the AFDS can command bank angles in excess of 15° before reaching Up + 20 knots. This reduces the overshoot protection normally provided by recommended maneuver speeds.
For flaps up maneuvering, maintain at least:

747-400
• "UP" or "UP + 20 knots" based upon gross weight

As for the low-speed, low-altitude turn, do we both agree that it will limit the bank to 15 degrees at V2 even with all engines operating? I have to admit that I've done this (inadvertently) on the classic and it won't limit the bank at V2 -- it will happily turn you at 25 degrees of bank. But, I was thinking the -400 AFDS would be a bit more thoughtful.

[Hardy Heinlin]

+90 might be a compromise between +80 and +100. I think I took +90 from a Lufthansa manual.


I don't think it will limit the bank to 15° at V2 with all engines operating. This would disagree with the texts and with your observation on the classic.

[emerydc8]

I was thinking the classic just wasn't that smart (you can't even engage the A/P until the flaps are up). It would be interesting to find out whether the -400 sim will let you do 25 degrees at V2 with all engines.

Do you still have the text that says it will not limit you to 15 with all engines operating?

[Hardy Heinlin]

No, I got that information from the discussion here last year.

But it's also in the texts you quoted yourself here:
http://aerowinx.com/board/index.php?topic=3154.msg36978#msg36978

[emerydc8]

Yes, it says that the AFDS limits the bank angle with an engine inop, but omits that part under the all-engines operating header. So I guess you could presume that it won't limit you to 15 degrees with the engines operating because of this omission.

Am I misreading Peter's reply that he agrees with my proposal? I know it's getting late over there.

I guess a better way to ask this is, will the auto position limit the bank to 15 degrees between V2 and V2 +10 regardless of whether you have an engine out.

- and with regard to your low speed low altitude turn, I think so, although it is very difficult to prove!

[Britjet]

The low-speed case is difficult for me to test in my sim sessions but the +90 case should be easier. I will try and look at it and report back.
I think the bank limit depends on whether you are in LNAV or HDG. Trainees were (and probably still are) told to look through the flight director and manually limit the bank to 15 degs when below +90 for selecting flaps up over 308T.
I'm afraid I can't remember the exact logic. I will try and grab a current 747 trainer this weekend and ask their opinion, and should be able to test it myself.

Peter.