737NG A/T & F/D GA Mode

[B737NG_Pilot]

With the A/T Arm switch at ARM, the A/T go–around mode is armed:
• when descending below 2000 feet RA
• when above 2000 feet RA with flaps not up or G/S captured
• with or without the AFDS engaged.

On my last flight, I was maintaing 2300RA with Flaps 1. The TMD was annunciation CRZ.

1) Shouldn't it be annunciating G/A?

2) If I just maintain 1900RA with Flaps up, will the TMD be G/A?

If both A/Ps are not engaged, a manual F/D only go–around is available under the following conditions:
• inflight below 2000 feet RA
• inflight above 2000 feet RA with flaps not up or G/S captured

3) why does it say descending for A/T & inflight for F/D Go-Around?

[B737900er]

Its talking about when TOGA is available. What you see on the TMA is just N1 limits. If you press TOGA it will then change to G/A.

Regarding the descending part - I believe its on the assumption your doing an Autoland and would be descending, where as in manual flight you could be straight and level for a bit.

[B737NG_Pilot]

Thanks for the reply 900ER.

G/A annunciates on the TMD only after Glide Scope Capture or at about 1800 RA for CDFA Approach.

However with flaps extended above 2000 feet RA, there is no A/T GA available. Why?

[repulo]

Hi 737 NG, I am sure once you have met the arming criteria for the TOGA bottoms and A/T is engaged, when pressing them you will have the A/T in GA.
As a sim instructor I realized that the sim doesn't always 100% reproduce aircraft behavior. This is due to different software or config differences. Just try it on a nice calm day in the A/C wit no traffic and push TOGA. Just remember to disengage the A/T immediately and recycle the F/D bars to open the speed window. Your bug will move slightly upwards too, so reset the target speed.

[B737900er]

With the amount of questions the OP asks on this forum, I Personally wouldn't let him loose on a bike, let alone punching in TOGA unnecessarily and expecting him to recover from it.

No offence.

[repulo]

There might be truth in your words.

[JeroenC]

Then answer his questions, if you know everything.

[B737NG_Pilot]

Repulo, 737900ER, I would be one of those, with whom you may leave your aircraft safely.

The questions, I ask on these forums, are because the system behavior is slightly different from what is mentioned in the FCOM. Specially with, systems related to auto flight. And I want to understand my a/c better.

Simple example, none of you could answer when does G/A annunciate on TMD. The A/T will never go into Go-Around mode, unless G/A annunciates on the TMD, irrespective of your RADIO ALTITUDE.

Please try this in your simulator or a/c.

Anyways, I appreciate your attempts to answer my doubts. No offense

[B737900er]

As mentioned in a previous post, that description is describing when TOGA is available.

[Jwscud]

With N1 selection in AUTO, the FMC switches to GA from CRZ on the TMD only when TOGA has been pushed. FCOM 2 11.31.32 is the reference. As regards "when descending below 2000ft RA", I think you are having an English comprehension issue. My reading is that the mode becomes active as the aircraft descends below 2000RA, not if the aircraft is in a descent below 2000RA.

[B737900er]

Further to the above comment, CRZ changes to G/A at Glide slope capture as well.

[Jwscud]

Indeed. Doesn't help that the two sentences are 7 chapters apart in the FCOM!

[B737NG_Pilot]

As per FCOM (FMC)

Below 2000 feet radio altitude, the FMC transitions to go-around logic from approach logic when any of the following events occur:

• pushing either TO/GA switch while in a descent

• executing a direct-to waypoint in the missed approach (other than the missed approach point)


As per FCOM (A/T)
With the A/T Arm switch at ARM, the A/T go–around mode is armed: when descending below 2000 feet RA .

My question is related to the A/T GA mode. If I maintain 1500RA in clean configuration, the TMD should be G/A. But it remains in CRZ.

[repulo]

I am going to spend the next three days in the SIM and will have a glance at the mentioned situation. I'll let you know, whereas I still think that my description earlier is correct.

[albertofdz]

Hi everbody

B737NG_PILOT, lets see if I can help with this matter.

The trouble with this system, is that it does get a little bit confusing., I think it helps to break up the involved systems... On one hand we have the A/T as part of the AFDS. The A/T will enter a thrust or speed mode.

On the other hand however, the A/T primarily uses LIMITS calculated by the FMC. (although, A/T can in fact receive other limits, in a degraded mode from the EEC, these are CLB, CRZ and REDUCED go around thrust, aka GA.

A/T G/A mode is ALWAYS (ILS and NON-ILS) armed in one of the 3 scenarios that you have correctly quoted. However, even though it is armed, it is not necessarily displayed. (The same occurs with the A/P go-around mode….. it arms, but it is not displayed!!).

Regarding the A/T LIMITS (provided by the FMC), the TMD will show G/A whenever a G/S is captured, obviously for an ILS approach.

On other types of approaches (VANV, IAN…) G/A will show on the TMD whenever the FMC transitions to a G/A. This will happen if the crew:
1. Does a "direct to" a point in the G/A
2. The system sequences a point in the G/A
3. TOGA is pushed
4. A climb is made at least at 600 FPM, whilst retracting flaps towards 15 (N) or 1 (N-1)

SO I hope these inputs have helped you.

Remember:

1. FMA shows A/T mode
2. TMD shows FMC thrust limit mode (A/T will never command more than this value)
3. G/A A/T MODE is only displayed when G/S is captured for an ILS approach
4. G/A A/T MODE is displayed when the FMC sequences to a go around mode (as seen above) for a non ILS approach.
5. TMD shows GA when an ILS G/S is captured
6. TMD shows GA when a non ILS approach sequences to a G/A (not before)
7. For a first push, A/T FMA mode shows GA
8. For a second push, A/T FMA mode shows N1.

* Regarding points 7 and 8, remember that the TMD will always show GA until a CLB mode is engaged.

Cheers!

[albertofdz]

Having said this, I know need help form somebody!!!

Also regarding the TMD….

According to BOEING, the A/T Go-around mode is terminated whenever:
1. A new pitch mode is SELECTED
2. ALT ACQ engages.

Additionally, BOEING tells us that if an A/P is engaged in CMD, pitch will engage in LVL CHG, and roll will engage in HDG SEL…

This last point greatly confuses me…. If I engage an A/P in CMD; does this mean that A/T GA mode will be terminated???? Or not…? (One thing is to SELECT a new pitch mode, and another thing is for the A/P to engage in command, and LVL CHG mode too will ENGAGE).

Not sure if my question is "understandable" Hope so!!!

Thanks

[repulo]

Sorry for the delay, couldn't try it in the SIM, had other things to do.

But I had a chance to try it in the A/C on a visual approach to Fuerte Ventura.
Condition:
- A/P engaged in V/s
- descending to 1600ft
- TMA in CRZ
- TOGA pressed at 1600 ft, TMA went into GA, A/P disengaged with the known
FMA annunciation.

So every thing went as already anticipated earlier, A/T has the same TOGA arming criteria like the A/P.

[repulo]

Alberto, if lvl change is engaged, its N1 limit is CLB. With some 737 even on T/O the TMA will go to CLB below thrust reduction alt if level change is pressed. It depends on the soft ware. We have one old A/C that has a different config since it is leased in that does that. Hope that helps.

[framer]

There are thousands of pilots out there who have insufficient tech knowledge and don't ask any questions. The OP consistently seeks more knowledge. We should never discourage that. Good on you mate, keep it up.

[albertofdz]

Repulo, thank you for you answer.

However i´m not convinced……. According to FCOM, during a go around, A/T GA mode ends when LVL CHG is SELECTED…..

If I happen to engage the A/P during said go around, LVL CHG will ENGAGE (also HDG SEL, unless LNAV was already engaged)…

You see, the trouble that i´m having is with the wording. If if engage an A/P, then LVL CHG will ENGAGE, and I mean ENGAGE, and not SELECT, I understand that it is not the same thing…. Does the system think like I do, or maybe not…?

So, if I engage an AP, perhaps TMD would still display GA rather than CLB (because I have NOT selected a pitch mode, instead, this mode has been engaged automatically) until a new pith mode is SELECTED, or ALT ACQ??? For me, this point is not clear at all in the FCOM..

Do you see were i´m going?

Sorry if i´m confusing you guys, and sorry for "beating around the bush", but I just like to have things crystal clear!

Cheers :D

[repulo]

Hallo Alberto,
when engaging the A/P after a GA the TMA will revert to climb, irrespective of the fact if level change was selected beforehand or not. To ease the understanding, just imagine what the designer thought: is the aircraft still in the TOGA mode, commanding all the known facts like climb rate, ground track, G/A power, etc,
OR is the aircraft in the climb mode, analog level change.
Hope that helps.

[latetonite]

To set things straight, I just tried it in the sim.

If, during a G/A, you select A/P in command, TMA remains G/A.
Only changes to climb if you manually select "N1", or automatic at acceleration altitude, if you have that option.

[albertofdz]

Hey latetonite and repulo,

You guys are awesome! Thanks for your answers.

So the system works just as I suspected.... Dammed "wording"!!!! As I said, SELECT, and ENGAGE aren't the same thing! Arrrrrrggggg

Cheers, great help chaps

[B737NG_Pilot]

Hey albertofdz, latetonite, repulo, framer and everyone else thanks for all your replies.

However my question only relates to the G/A annunciation on the TMD.

During my last few flights, I was able observe the following.
a) Level Flight at 1900 RA (Flaps UP, TMD: CRZ).

b) Level Flight at 1800 RA (Flaps UP, TMD: G/A).

This answers the following when descending below 2000 feet RA, A/T go–around mode is armed.

However,

a) Level Flight at 2400 RA (Flaps 05, TMD: CRZ)

This fails to answer when above 2000 feet RA with flaps not up . How above are we looking at?

Please note, that I have tried these on 700/800/900ER Series of Aircrafts. The result was same. No approach was being conducted.

Once, again I really appreciate, all of your efforts.

[latetonite]

Hello B737NG,

The GA being armed above 2000 ft, flaps selected, seems to be an option, in the software your operator uses.

[repulo]

Hi again 737NG,

first, I enjoy talking about these subjects since there is always something I haven't thought about, even after being on the NG since it was first delivered to my company in 1999.
As it was mentioned beforehand, there are several customer options, eg we are having 6 fix pages, IAN enabled... So we might fly the same aircraft but observe slightly different annunciation.
In our config, TMA remained in CRZ at 1600' AGL in the clean config. I might have a chance to try the GA AP engaged situation on Sunday, depends on ATC on my way to LPA.
I don't trust the SIM, it does not always represent the company config by 100%. And usually it's exactly these little gimmicks that are concerned.

[repulo]

OK Gentlemen,
here is the final answer to your questions: Had a chance to try the scenario yesterday on a visual approach to LPA. (Quite nasty wx with wind gusting to 45 kts..)
Condition: FD on, MCP speed and VS being the active mode. Missed app alt of 4000' set. Pressing TOGA, TMA goes to GA, as said before. Then AP selected, level change and heading select becomes the active mode. And the TMA? It goes to climb as I said before. Now if some of you observe different things in the SIM, probably it's a programming fault, I don't think that the NG's of different companies have substantial software differences.
Somebody mentioned earlier that the thrust reduction alt can be programmed, I don't think that that is an option for the GA, just for the T/O. GA thrust limit is very much the same value as max cont thrust so no need to hurry.

[latetonite]

Hi repulo. What altitude you pushed G/A?

[repulo]

At around 2000' MSL over the sea, so RA also around 2000.

[latetonite]

Your default thrust reduction is, Just like TO, probably 1500 ft, right?

[repulo]

There is no default thrust reduction on GA. Read my post above.

[latetonite]

Correct, Repulo. I let it slip so early in the morning. GA mode terminates when a different pitch mode is selected, or Alt Acq.

[Bob Lorentz]

Hi B737NG_Pilot,

I think albertofdz pointed you in the right direction: you might be confusing N1 limits (TMD) and A/T modes (FMA).

The conditions you name from the FCOM are related to the A/T mode, e.g. the left indication of the FMA. Your observations in the A/C seem to be of the TMD, which represents the current active N1 limit.

Correct me if I missed the point.