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FCU Altimeter Setting

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FCU Altimeter Setting

Old 8th Feb 2014, 13:38
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FCU Altitude Selection

Our Company has decided to change the Airbus SOP so that ALT selections on the FCU will be made in 100ft increments (for "safety Considerations"). I have scratched my head for some weeks to understand the dangers of setting the ALT in 1000s as we have always done, but have drawn a blank. Does any other Airbus operator use this method or perhaps I am missing the obvious.

Last edited by Capt Scribble; 9th Feb 2014 at 15:24.
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Old 8th Feb 2014, 13:42
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Could be more hazardous as the panel will be taking the pf out the loop for much longer?
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Old 8th Feb 2014, 13:46
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Some airlines have this for specific flight phases, like below transition level or below MSA.

Making use of it on a continuous basis is plain stupid. Another management powertrip idea, like a dog pi$$ing on a lamp post to mark the territory... Companies are full of these, trying to re-invent the wheel -or teaching birds how to fly- in order to justify their positions...

By putting more rules, we ask pilots to follow blindly and this decreases airmanship and initiative. Any professional pilot will use good judgment to find out when using 100's or 1000's is more relevant to the task at hand.

Last edited by FLEXPWR; 8th Feb 2014 at 13:49. Reason: additional input
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Old 8th Feb 2014, 14:41
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Our company's SOP is to use the 100's setting below transition altitude and the 1000's setting when above it for flight levels.

Doesn't seem to be much of a problem - only takes a second to switch it over.

But Capt scribble, are you saying that ALL your selections must use 100's ? If so, that seems a bit weird. Ten times the number of turns to dial in a big climb ? Pointless and stupid, it won't make selections more 'safe, it will add extra errors because you will have to spin that knob so much that it will probably actually reduce precision.
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Old 8th Feb 2014, 14:58
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Ha, I guess you don't have to fly to countries that use meters...

Usually such rules or procedures are born from somebody's major screw up....did something happen recently within your company that prompted this as a the solution?
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Old 8th Feb 2014, 15:32
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Uplinker, Yes, we used to use 100s with altitude but now its all the time. As this change is allegedly for safety, I just wondered whether anyone else world wide found setting in 1000s a great risk. By the time I get to the Alt, I'm likely to have forgotten what it was.
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Old 8th Feb 2014, 20:53
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If you are cleared for FL320 and you turn the rotary selector just 1 click too far you would have entered FL330 iso FL320 when 1,000ft increments are selected. During phases of high workload, such an error could remain undetected.

With 100ft increments, the selected level would be FL321, which does not look right at all. Therefore, the 100 ft setting increases your chances to notice some fingertrouble.

Of course we are talking of propablities of 10E-x.
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Old 9th Feb 2014, 05:57
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There is no standard procedure. But generally below TL or FL100 it is changed to 100s because you can get intermidiate altitudes like 3700ft etc. Also it mitigates the error, mistake in 1000s can easily be below ground level. Some always leave it in 100s but use as required basis but come back to 100s. Using it in 100s only is not logical nor practical.
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Old 9th Feb 2014, 09:52
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Why not get the PNF to confirm the selection? That way, not only is e selection checked, but also a common understanding of the cleared level that was read back by the PNF. Useful in parts of the world where comms are difficult.

'Just one click' doesn't wash, as a crew should pick up on the fact they have been cleared a nonstandard level.

Not to forget mode s provides yet another level of protection, albeit not universal yet. The distraction of using hundreds I don't like.
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Old 9th Feb 2014, 10:57
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I have scratched my head for some weeks to understand the dangers of setting the ALT in 1000s as we have always done, but have drawn a blank.
This is nothing new; various airlines have tried to re-invent the wheel and discovered (usually the hard way) that square wheels don't work.

What about an emergency descent? If you reach up to the altitude select knob (with it set to 100's at cruise level) and give it an anti-clockwise twist, then pull, descent will be initiated, but here is my guess at what will happen next -
  • you will pull heading and speed, each in turn
  • you will read the FMA, and perhaps be comforted by the "THR IDLE, OPEN DES. HDG" that you see
  • you will then deploy the speedbrake
  • at about this point you will go into ALT* with full speedbrake at high altitude
  • you will utter #$%^&*()

The suggestion to use 100's below the transition level and 1000's above would seem to have considered the above scenario, where perhaps your company has not.

If you are cleared for FL320 and you turn the rotary selector just 1 click too far you would have entered FL330 iso FL320 when 1,000ft increments are selected. During phases of high workload, such an error could remain undetected.
Errr....whatever happened to reading the FMA?

Why not get the PNF to confirm the selection?
One would sort of hope that they do this already.......

Last edited by chimbu warrior; 9th Feb 2014 at 10:59. Reason: for clarity
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Old 9th Feb 2014, 11:08
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Using the hundreds setting to change the selected altitude all the way up to the cruise alt and back again will wear the mechanism out prematurely.

We had proponents of this idea as far back as 1988/9 on the A320. The argument in favour was that, at the end of a given selection when you push or pull the knob, you can accidentally click it one notch clockwise or anti-clockwise without realising it. When the setting is on hundreds, that mistake only changes the selection by a hundred feet instead of a thousand.

Some of the guys that came on to the A320 fleet from the B737 and B757 seemed to be particularly susceptible to making this mistake. The reason was that they were used to having the altitude window on the FCU as the only indicator of the selected altitude, and were reluctant to change the habits of a lifetime.

The solution to the problem, of course, is to use the selected altitude indication on the PFD, not the one on the FCU. That way, you will pick up the mistake immediately. In fact, once you have found the right knob, the whole operation should be performed using the PFD indications. (And the same philosophy applies equally to the VS/FPA knob, not to mention the SPD/MACH and HDG/TRK knobs.)

The bottom line is: at the moment you push or pull the altitude selector knob, you MUST be looking at your PFD, not the FCU.

Last edited by Chris Scott; 9th Feb 2014 at 15:06. Reason: Forgot the SPD/MACH knob...
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Old 9th Feb 2014, 11:37
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Agreed chris scott

What that man said... ! The PFD is where you should look to confirm the selection .. Not the FCU .. For all modes selected ...that is the philosophy of the FMA wja
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Old 9th Feb 2014, 11:49
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Thanks, woodja51,

Some of our trainers used to cover up the FCU windows (on the simulator) to stop guys using them...
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Old 9th Feb 2014, 14:19
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Some trainers still do.....
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Old 9th Feb 2014, 14:52
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An interesting discussion. I am not familiar with the particular equipment, but would it be correct to assume that there is both an ALT SEL readout on the FCU near the selector, and a readout on the PFD ?

If so, this follows general design principles (SAE S7 recommendations circa 80/90s), where annunciations should be provided both at the point of selection (next to the knob) and at ‘the point of operation’ (PFD for inst flying / monitoring).

The current use of these systems appears to contradict the design assumptions; apparently due to the risk of mis selection. Thus if true, procedures have been introduced to overcome a design weakness, yet we have to and can accommodate many weaknesses because no system is perfect, but this should not be at the expense of introducing another error: – reaching for the selector knob without looking and choosing an incorrect control; or looking at the selector then back to the PFD with associated increased workload.
There may be no answer to such dilemmas, but it would be interesting to understand some of the rationale and balancing safety cases.
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Old 9th Feb 2014, 15:04
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Well, thank the Lord for that. It would be rather sad (although not in the least surprising), if the lessons we learned 25 years ago had been lost by our successors...

Cap'n Scribble, Zirrr,

Can I respectfully ask you to amend your thread title to something a bit less confusing? "FCU Altitude Selections", perhaps? At first I thought you were on about the altimeter sub-scale (hPa/inHg) selector.
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Old 9th Feb 2014, 15:53
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Chris Scott
What you said is perfect. That is the way to fly Airbus FBW.
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Old 9th Feb 2014, 16:27
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Hi PEI_3727,

Your reference to SAE recommendations is interesting, but I'm afraid your being "unfamiliar with the particular equipment" shows clearly when you go on to remark that:
"[...] but this should not be at the expense of introducing another error: – reaching for the selector knob without looking and choosing an incorrect control; or looking at the selector then back to the PFD with associated increased workload."

So let me explain the situation from basic principles (A320/330/340/380 pilots can go off and make a cup of tea, and/or concentrate on the Six Nations rugby match).

When the AP is engaged, the PF makes his/her own altitude selections using the selector knob on the FCU. (S)He must monitor the flight-path on the PFD and ND (nav display), and - in climb or descent - needs to minimise the amount of time looking at other parts of the cockpit. The PNF monitors the selections made by the PF, and - when they have been completed - calls the associated FMA changes (i.e., any required by company SOPs) as seen on his/her PFD.

So: back to the selection itself, in this case an altitude or flight-level change. The PF switches his gaze from the PFD up and across to the FCU, and reaches for what he thinks is the altitude selector knob. Touching the knob but not yet moving it, he averts his gaze back to the PFD. The values of the 4 parameters that can be adjusted by the 4 FCU knobs - SPD/MACH, HDG/TRK, ALT, and VS/FPA - are all visible on the PFD in one form or another.

The PF turns the altitude knob, simultaneously observing the changing value of selected altitude or FL. If he is turning the wrong knob, this will be apparent immediately. (The easiest pair of parameters to mis-identify on the FCU itself are the adjacent SPD and HDG knobs, whose associated read-out windows both show three-digit values. On the PFD, the parameters cannot be confused.)

Finally, the PF pushes or pulls the knob, depending on what type of climb or descent he wants (or leaves it alone if he wants to use VS or FPA). Now for the crucial bit. The PF continues to watch the selected altitude until his hand is well clear of the selector knob, to ensure that he has not inadvertently turned it. The PNF can now announce the FMA visible on his PFD, e.,g.: "Open-descent flight-level two-four-zero."

When the PF is hand-flying, the selection roles are reversed, except that, if the FD is being used, the PF first has to tell the PNF what (s)he wants; e.g., (s)he might want a change from managed-descent to open-descent, or even VS or FPA. That increases the workload for both pilots.

To sum-up, PEI_3727, there is no harm in choosing the wrong knob, provided you don't turn it until you are watching its effects on the PFD. And the less time your eyes are away from the PFD, the less likely you are to deviate from the intended flight parameters.
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Old 9th Feb 2014, 22:56
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At my company, the PM makes all altitude selections, never the PF. Both pilots will then call out the new altitude.


Note...I don't fly Airbii
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Old 10th Feb 2014, 02:34
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Check Airman
PF handles FCU unless he is flying manually or in some extra ordinary case. If your company wants PM to handle FCU even on AP then your company procedure is against the principle of Airbus flying. Since you are not AB pilot you may have misunderstood.
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