A320 - Arming Approach

[Bubi352]

In the Airbus you can activate the approach at any altitude but I was told if you arm (APPR on FCU) the approach above 8,000 ft AGL, the autopilot and FDs disconnect. Does anyone have a reference for it?

[3 Point]

Doesn't happen else how would you land at a high altitude airport? We used to operate A320s in Addis Ababa at 7,800' elevation! It will take the FMS to approach phase which could be awkward if you do it by mistake in the cruise; to get back to the cruise phase just re-enter the cost index.

It's been a while and two new type ratings since I flew the Airbus so don't take my word for it and I can't give a reference but I'm sure that others will answer and either confirm of dispute what I say. Either way, enjoy the 'Bus, it's great!!

Happy landings:):)

[Bubi352]

It's apparently a function of AGL not MSL. I was told if you were on an ILS above 8,000 AGL and were to arm the approach on the FCU, the autopilot would disengage and the FDs disappear. It's actually valid for any instrument approach. I haven't found any reference to it nor tried it. I was hoping someone could confirm this.

[3 Point]

AGL versus MSL; could be but I have no memory of this. I'm sure I have armed approach this early with no ill effects before but we'd best wait till a current 'Bus driver responds rather than cloud the issue with my half remembrances!

I'll lurk and look out for a more complete answer to appear.

Happy landings!

[CONF iture]

It's apparently a function of AGL not MSL. I was told if you were on an ILS above 8,000 AGL and were to arm the approach on the FCU, the autopilot would disengage and the FDs disappear.
All I can read in the FCOM 4 is the following :

http://i65.servimg.com/u/f65/11/75/17/84/cx_02510.gif (http://www.servimg.com/image_preview.php?i=56&u=11751784)


But maybe not the best procedure to arm an ILS too early as spurious or false capture for LOC and/or G/S may occur.
RNAV is a different matter, and I can remember arming RNAV approach well above 10000 feet with no adverse consequence.

[ggofpac]

ermm...but why arm app mode when that far out? 8000= 24 +++ nm. Just outside the 25nm localiser "limitation"?:confused:

[BadAndy]

Saw this thread yesterday. Tried it today to see what would happen. Armed approach out of 16,000' (9800' AGL) when cleared for the approach. Worked just fine. Stayed at CAT I until around 8000' AGL then went to CAT 3 automatically.

[TO MEMO]

The other day we armed APP while at FL350. No AP disengagement...
Normal behavior.

cheers

[zonnair]

Just curious... Why do you arm your APPR at FL350?

[NVpilot]

zonnair, I assume he tested the system to answer the first posters question, no one uses this as a normal procedure.

[Bubi352]

This discussion came up supposedly because someone armed APPR the approach on a very long final. The autopilot and FDs apparently went OFF as a result. This is a 'story' that was passed along from pilot to pilot. You know how it goes... I wanted to see if there was any validity to it. I am waiting for my recurrent this week to try it also. I appreciate guys!

[Admiral346]

When training on the 320 my instructor told me this:

He thought if the flight path is all programmed in, and the aircraft will follow it until the intercept of the ILS, why not press the APP button early? - It is very dangerous, because the ILS reciever then controls the aircraft movement (speaking figuratively) if it recieves anything. So pressing it over the Atlantic would probably do nothing, but pressing it anywhere where you might recieve a signal of the same frequency as the ILS you intended to intercept will cause a capture. That might have some negative side effects cruising at FL350, if the machine pitches down and starts turning...

What you are doing is escentially giving radio signals a higher priority than the FMS signals towards the autopilot.

Boys, it is not a toy!

Nic

[Sir Herbert Gussett]

To give it a try? Are you lot mad? I hope that was done in a simulator and not with paying passengers on board! You are paid to fly from A to B as quickly as possible, and as safely as possible - not faff about as a test pilot playing with your huge toy!!!

[Admiral346]

Well, Sir Herbert, I agree, you just used different words!

I can remember arming RNAV approach well above 10000 feet with no adverse consequence - that is no problem, as I explained above, because the FMS will just fly whatever you programmed into it.

You guys should be flying something that has the pilot make the choice of "NavSource", like my little CRJ. That makes it obvious what kind of signal is being used to compute autopilot commands.

Nic

[Virtual Reality]

Our SOP says:-

The APPR pb shall not be pressed until:

• The ILS is tuned and identified.
• Clearance for the approach has been received.
• The aircraft is on an acceptable intercept heading.
• Raw data confirms correct sensing.
• The aircraft is not laterally displaced to the extent that a false capture may occur.

Certainly 25 nm ICAO ILS protection zone is to be observed.


VR :cool:

[CONF iture]

To give it a try? Are you lot mad? I hope that was done in a simulator and not with paying passengers on board! You are paid to fly from A to B as quickly as possible, and as safely as possible - not faff about as a test pilot playing with your huge toy!!!
There is no panic to have here. It is not question to intentionally shut off one hydraulic system or shut down one engine. You are paid also to know how your aircraft works, and the question Bubi352 was presenting is absolutely legitimate and a clear sign of interest for better knowledge.
There is a multitude of stuff you can try in flight with absolutely no ill effect, as long as it does not compromise the safety of the flight. Of course, both crew members must be involved in the process.
Is there a danger to give it a try and arm the approach at 20000 feet, absolutely none, as long as you're ready to intervene if the aircraft is not doing what you expect him to do.

[Admiral346]

Confiture,
well at 20000' it may be recoverable. But maybe is a pretty bad word in the way I operate an airliner.
At FL350, as the boys wrote, it might dive you into a highspeed stall, intervene with traffic below. You have people walking, trolleys loose, hot drinks being served, and you would risk the jerk of a sudden intercept? Quite dangerous, I'd say.
What's so hard to understand about this problem? The ILS reciever becomes "hot" upon pressing that button, AND having an ILS approach programmed into the FMS. Any signal of the same frequency as the preprogrammed ILS will trigger an intercept, if strong enough. The FMS and the ILS reciever are intermingled on this aircraft.

No toy, I'll stick with that!

Nic

[jtr]

At FL350, as the boys wrote, it might dive you into a highspeed stall, intervene with traffic below. You have people walking, trolleys loose, hot drinks being served, and you would risk the jerk of a sudden intercept? Quite dangerous, I'd say.

If that were the case it would be a "guarded" switch or require a confirmation press after the initial. I have seen it pressed accidentally as the result of a slip of the hand in turb.

[PENKO]

Whilst not wanting to sound overly dramatic, I would be rather concerned if my colleague started arming approach at FL350! If the question is to find out if the thing will arm above 8000 feet, then fine, arm it passing FL100 or so, where I'm pretty sure I can handle most AP-malfunctionings without raising my bloodpressure. But to go experimenting with mode selections in cruise where your options are somewhat limited should anything go wrong, does not make me feel very comfortable.

In these electronic jets, little things sometimes have big consequences! So yes jtr, I agree that the APPR pb is not guarded. But do you want to be the one to find out there is some undiscovered programming glitch? (like the guys who found out that in some cases after arming approach, the aircraft will not pitch up during the subsequent go around, in stead heading steadily towards the ground at increasing speed)

[TO MEMO]

Dear PENKO, ZONNAIR, NVpilot,

As said by NVpilot, I did armed it in flight (not a simulator) at FL350 to test it after reading the original post.

Saying that that is dangerous, people moving in the plane, bla bla, bla bla, is stupid. Those of you who alledged that what I did is dangerous, you have no idea of how the system works... and that is dangerous!

APP briefly armed at FL350 (as it was the case) will do nothing! Even if you do by coincidence have an ILS frequency in the area where you are equal to the one you entered in RADNAV page, and the aircraft receives it at FL350 and captures it, then the only thing you have to do is press ALT or pull HGD. That`s it!

And no, it will not pitch down, because it will do LOC* before...

And here is another hint! Press ILS switch on FCU, as I did... and if you see no LOC or GS indication... the aircraft is not receiving any ILS signal, hence it will capture nothing!

So dangerous what I did...:ok:

Cheers

[PENKO]

Mig3, that's another incident. I am talking about the reason you have to deselect approach after becoming visual before disconnecting the AP, as per the airbus OEB. (too lazy to look up the number, if it rings a bell, you know what I am referring to)


Zoneair, did you ever hear of the DC10 crew that thought it pretty harmless to pull a CB for some engine indicator at cruising altitude? They blew up an engine in the proces, tearing a hole in the fuselage, killing a passenger. I'm not saying arming approach will have that effect in the cruise, but you just don't know for sure whatever undiscovered glitch you might encounter. Cruise level is not the place to experiment if you ask me.

[rudderrudderrat]

Hi,

I don't think there is anything on the MCP which will blow holes in an aeroplane. If the designers hadn't tested the effects of a mistaken button press whilst the aircraft was in the cruise - then it would never have been certified.

There is always the big red button which would prevent the "wrong" button press from developing too far.

[PENKO]

OEB 188/2
One Operator reported a case where the flight crew initiated a Go Around slightly below the Minimum Descent Altitude (MDA), and the aircraft didnot pitch up as expected. The flight crew performed a non precision approach (a VORDME approach) using the FINAL APP managed guidance mode with the AP1 (Autopilot) engaged during the final approach. This OEB is issued to provide flight crews with an operational procedure to avoid such aircraft behavior. The operational procedure provided in this OEB applies to all Non Precision Approaches, for both conventional approaches and RNAV approaches, flown in FINAL APP managed guidance mode.

Rudderrat, please tell us which other glitches the elaborate testing program has not yet discovered! I'm not being paranoid or anything, all I'm saying is that the button is not meant to be pressed at FL350, and that I don't want to be the one that finds out there might be a problem doing so anyway. :ok:

[rudderrudderrat]

Hi Penko,

The big red button and manually pitching up would definitely solve the problem you mention above. The autopilot doesn't have to be in control all the time.

There are probably more glitches waiting to be found - besides the severe reset of both FMGCs if your fix radial happens to cross the final approach track etc.

[charlies angel]

PENKO
I think your lack of ambition to fully understand the nuances and complexities of an aircraft that you (presumably) fly extremely worrying.
The OEB you allude to is concerning go/around from a fully managed NPA not a precision approach so irrelevant to anyone with a basic understanding of Airbus.
Tell me does a managed VOR approach fly down the green line,the GPS derived track to touchdown,the inbound course from the RADNAV page?
In an FMS2 aircraft for example (if you can be bothered to check!) the RADNAV page does not tune to the approach ILS frequency until within 250nm to touchdown(or is it track miles,or direct?) so will arming the approach actually do anything outside 250nm?
On your autoland does the aircraft yaw on landing with reference to its last GPS derived track to touchdown, or does it yaw in relation to the inbound course you (presumably) checked at 700'? Does it change if the aircraft is CPIPS1 or 3,FMS1 or 2 ,honeywell or collins equipment?
This is not a Cessna 150 my friend, it is a COMPLEX MACHINE.Lack of technical knowledge has caused many many accidents amongst the "whats it doing now" brigade.
If you cant be bothered to get your head in the books and merely want to push some coloured buttons go and work at Tesco check out:O

[PENKO]

Angel, if you spend as much time reading FCOM as trying to understand what I'm actually saying in my post, you would not have wasted your time typing a message that really only says: 'look how smart I think I am'.

I don't wish to enter a contest to see who can pee the further. But, there is an old saying in aviation, older than any Airbus. It's about old pilots and bold pilots. Heard of it? We'll that's basically all I'm saying. We've all seen planes do things they're not supposed to do, and things we thought it was not supposed to do. So stick to what you know as much as possible and leave experimenting high up in the stratosphere to Jean Claude of Toulouse!

But thanks anyway for those little techy facts, I was feeling quite bored and unchallenged after completing my six monthly tech questionnaire, so now I have some new things to look up. Very grateful sir/madam. Not sure I'll bother about the Collins stuff though!

[charlies angel]

aah tech refreshers...better than Horlicks.....just off to figure out how the sky+ thingamagig works LOL :ok: