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Old 7th Jun 2011, 13:58   #1 (permalink)
 
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A320 the big flaw of the UNRELIABLE SPEED/ADR CHECK procedure

After studying the issue for years (not only the procedure but also the FCTM, other airbus publications, powerpoint presentations) and over two hours of LPC simulator dedicated to this issue, I have come to the conclusion that there is a big flaw on it:

How can we tell if the altitude information is affected or not???

The procedure will soon lead you to this. Inmediately if "safe conduct of the flight" is not affected or after the memory items if it is:

LEVEL OFF for trouble shooting

HOW ON EARTH CAN I DO THAT IF I DON'T RELY ON THE DAMNED ALTIMETEEEEEERS???

I don't have GPS in my fleet, right now. Nor I have that new gadget, the BUSS, which looks like a very good thing and apparently is fitted in the 380s.

Is there any method to determine if the static part of the air data is OK or not?

I mean: are there different modes of static air data failure? Or there is only one mode, where V/S remains zero no matter how fast you climb or descend and then is totally obvious that static data is un reliable?

By the way, I never have this problem in the sim because it cannot simulate problems in the static. only in the pitot.
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Old 7th Jun 2011, 14:00   #2 (permalink)
 
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You assume a pitch and power setting which should result in level flight, and you look out of the window.
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Old 7th Jun 2011, 15:40   #3 (permalink)
 
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I believe most a/c with IRUs use them for V/S instead of static.

Interestingly, a pneumatic IVSI, Instantaneous Vertical Speed Indicator, contains a small pendulum that starts tne needle in the correct direction to counter the delay inherent in the basic VSI.

GB

Last edited by Graybeard; 7th Jun 2011 at 16:24. Reason: correction for IVSI
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Old 7th Jun 2011, 15:58   #4 (permalink)
 
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Most ADRs use a combination of baro and IRS information to resolve VS. And a VSI with the pendulum is called an ILVSI. IL standing for Inertial Lead.
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Old 7th Jun 2011, 16:12   #5 (permalink)
 
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My company's QRH doesn't have any procedure for Unreliable Airspeed in cruise, only during initial climb. Seems like another hole in the Swiss cheese.
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Old 7th Jun 2011, 16:25   #6 (permalink)
 
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scary comment above!
We have had some quite intensive training in this stuff over the last year, apart from regarding the basic pitch/power settings as memory items, we are advised to crosscheck alt with the GPS output.
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Old 7th Jun 2011, 16:28   #7 (permalink)
 
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Thanks for the correction, Dan. I went back and completed and clarified my post.

GB
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Old 7th Jun 2011, 17:13   #8 (permalink)
 
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the other flaw is

what the heck is "if safe conduct of the flight is affected"

In my opinion, every time you have an unreliable speed safety is inherently affected. For all you know, you could be on the verge of stall, or overspeed, or a spiral dive or whatever.

If you have unreliable speed at 390, in turbulence at night with hail hitting the windshield, your body giving you all kind of misleading inputs to your brain... Is the safe conduct of the flight affected? I would say "yes it is" so i would have to take over manually and set pitch at 5 and CLB thrust? I don't think so...

They have to enhance the procedure (maybe including more "emergency" pitch-thrust settings: for high level climb, cruise or descend. These are on the tables but not on the memory items.

They can also develop a tool to give inertial V/S in the MCDU (altitude is secondary. V/S is what we need)

Then we can always level off.

One last thought:
What if the Air France 330 was in overspeed, or even well beyond it and when AP disconnected they set 5 up all of a sudden? let's say a 4 increment in pitch at that level and that speed. This could explain the pitch up input.
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Old 7th Jun 2011, 18:13   #9 (permalink)
 
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Quote:
They can also develop a tool to give inertial V/S in the MCDU
Inertial VS doesn't work without barometric inputs. See:

FPV and FPV Cage
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Old 7th Jun 2011, 22:48   #10 (permalink)
 
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From the 744 ground school notes.

Quote:
The IRU must get valid pressure altitude from the ADC to compute vertical speed.
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Old 8th Jun 2011, 17:52   #11 (permalink)
 
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If there are accelerometers and valid aTTitude, inertial V/S is easy to obtain.

Or they can install a dedicated accelerometer. There must be a thousand ways of achieving a reliable instrument to achieve zero vertical speed.

Or else, enlighten us how to rule out (or not) failed altitude/V/S data
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Old 9th Jun 2011, 11:22   #12 (permalink)
 
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Quote:
If there are accelerometers and valid aTTitude, inertial V/S is easy to obtain.
No, it isn't. See the thread discussion quoted above.
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Old 10th Jun 2011, 09:35   #13 (permalink)
 
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On a recent A320 sim-check, we had the following scenario :

In T/O just after rotation, we got 2 unreliable ADR`s, that both had the same failure of increasing airspeed, rapidly increasing to above 400 kts.

That means, that even though they are faulty, they wote out the remaining good ADR.

And what happens on the A320 in an overspeed situation : VMO/MMO + xx kts/0.xx mach, the A/C starts to pitch up, even though you manually try to pitch down !

And even more scary, with A/THR engaged, it reduce to idle due to higher speed than targetspeed. (We are not quite sure if this a "simulator thing" that it reduces to idle, can`t find anything about it in the books. Anyone confirm ??)

So with a rapidly increasing pitch and thrust at idle, things start to evolve very very quickly ! (and in this scenario very close to the ground). You have to do the following quickly, not a memory item (we are talking seconds) :

Solution : Select 2 ADR`s to off (doesn`t mean anything which two) and then you can apply the pitch/power procedure.
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Old 10th Jun 2011, 16:39   #14 (permalink)
 
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hadn't thought of that one!

regarding the thrust, if in SPEED, thrust will kept at idle as long as speed is much faster than target.

So in this case the high speed protection is trying to kill us. Taking over manually solves the A/THR comanding idle thrust problem, but what about the high speed protection!

how come thre is nothing in the procedure about this? what are we missing?

after rejecting one ADR we still have normal law, so it makes sense.
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Old 10th Jun 2011, 17:29   #15 (permalink)
 
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In Normal Law, Alpha ('Stall') protection "overrides" High Speed protection.

In Alternate Law, if High Speed protection is available (it is not always), it is "reduced", which means (IIRC) you can "overpower" it with e.g. full fwd stick.

Thus within the Flt Ctrl Laws, the High Speed protection should not be able to pull the nose up into/beyond the stall.

Of course, other factors e.g. THS position, CG, further malfunctions, Crew reaction time, may mean a stall can occur... all I am saying is the simple "aircraft uncontrollably pitched up into a stall and nothing anyone could do about it" line is not 100% valid

NB I am talking A320 series here - A330 may be different (but doubt it fundamentally).
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Old 10th Jun 2011, 17:35   #16 (permalink)
 
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Why do people get wound up about unreliable airspeed in the cruise?

When you get to cruise make a note of the pitch attitude and N1 setting?

If you get Unreliable airspeed, you have the couple that was working fine to start with.

Or turn to 2.21 of the QRH, go to the bottom of the page and cross reference......

CLEAN - FL - SPEED - WEIGHT - PITCH/THRUST at your current weight.

Read across the pitch/thrust tables until yours match! Its all in front of you and always has been.

(While you're at it, note the LRC and green dot driftdown flight levels in case.)
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Old 10th Jun 2011, 19:38   #17 (permalink)
 
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Of course

Im sure that maintaining altitude with 2.5 or 3 degrees and about 85% N1 will give you about .76 at most of the typical flight levels and weights in cruise.

But they should include a pitch and thrust for cruise in the memory items.

And the level off critical question remains?

"Am I levelling off or is something in the air data system fooling me and leading me to disaster?"

I wonder if there is any means (other than GPS) to rule out a problem in altitude indication before leveling off for the trouble shooting
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Old 11th Jun 2011, 07:58   #18 (permalink)
 
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Hi Microburst2002,
Quote:
By the way, I never have this problem in the sim because it cannot simulate problems in the static. only in the pitot.
I think this is because, pitots can clog with ice, nesting wasps, bird strike, or be unreliable with radome damage etc.
The only static ports problem I can think of is if they have been taped over by maintenance / engineering. Your outside check before flight should prevent the last case.

Otherwise if IMC, and no GPS data - I can't see how you would determine if you have levelled off either.

Last edited by rudderrudderrat; 12th Jun 2011 at 14:56. Reason: plural static ports
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Old 11th Jun 2011, 10:33   #19 (permalink)
 
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For me, the "level off" part means you are not climbing/descending at XXXX ft/min, which could affect your speed (a'la AF447's climb at 7000ft/min). Setting pitch at ~2.5 deg and thrust of 85% (or the pitch/thrust setting from the QRH), ensures that you are leveled off, or at least close enough for practical purposes and is more important than what the altimiter says. Even if you have one, you should hold the pitch, power, not the altitude...

Last edited by Stuck_in_an_ATR; 11th Jun 2011 at 10:44.
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Old 11th Jun 2011, 10:43   #20 (permalink)
 
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Setting 2.5Deg pitch and 85% N1 close to coffin corner and slow on speed, hockey stick territory (which you wouldn't know if you didn't have the cue of yoke pressure) will not suffice in recovering the situation.

Therefore holding the pitch to recover the stall isn't always best advice especially at high alt with little margins
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