BUSS FL250

[Lantirn]

In unreliable speed (all ADR's affected) you have to descend to FL250 to enable BUSS.

However in triple ADR fault, executing the ALL ADR OFF procedure, there is no need to descend to FL250 for BUSS switching. Or at least it is not documented in the QRH or in the ECAM.

I know that the BUSS is valid below FL250 due to mach number effects in AOA vanes.

Any input?

[Zaphod Beblebrox]

This is news to me... i work for an airline with lots of Airbus Airplanes.

QRH page 123, amended 01, Oct. 16states:

All ADR Off: "BUSS equipped aircraft when require by the ECAM NAV ADR 1+2+3 FAULT procedure."

1. SPD......................................................... .....................FLY THE GREEN
2. MODE SEL......................................................... ..........MAN
3. MAN V/S CTL......................................................... ......AS REQRD
for aprroach
4. SPD......................................................... ......................FLY THE GREEN
5. FOR LNG......................................................... ..............USE FLAPS 3
6. GPWS LDG FLAP 3.........................................................ON
7. landing distance procedures apply
8. APPR SPD......................................................... .............FLY THE BUG


it don't say nuthin about descending to FL 250???

[Starbear]

This is news to me... i work for an airline with lots of Airbus Airplanes.

QRH page 123, amended 01, Oct. 16states:

All ADR Off: "BUSS equipped aircraft when require by the ECAM NAV ADR 1+2+3 FAULT procedure."

1. SPD......................................................... .....................FLY THE GREEN
2. MODE SEL......................................................... ..........MAN
3. MAN V/S CTL......................................................... ......AS REQRD
for aprroach
4. SPD......................................................... ......................FLY THE GREEN
5. FOR LNG......................................................... ..............USE FLAPS 3
6. GPWS LDG FLAP 3.........................................................ON
7. landing distance procedures apply
8. APPR SPD......................................................... .............FLY THE BUG


it don't say nuthin about descending to FL 250??? Zaphod, I suspect that's because you are looking at only the ALL ADR OFF situation. Look at the Unreliable Airspeed: It still retains the FL250 caveat.

Lantirn:

My understanding was that FL250 was chosen for certification for the Unreliable Airspeed situation because "most" incidents were caused by icing of probes and most cases this was resolved fairly quickly once probe heat (and maybe descent) overcame the ice and so normal indications would return and could be used However if airspeed was still unreliable below FL250 then issue was most likely not caused by ice (maybe damage) and hence use of BUSS thereafter. One ADR is retained above FL250 if possible for stall warning. Additionally I understand that Airbus were planning certify BUSS use at all altitudes and perhaps they have now but the unreliable airspeed procedure still retains FL250 as they would like you to have normal airspeed indications if at all possible rather than reverting to BUSS immediately.

I also work for an airline with lots of Airbus types.

[Zaphod Beblebrox]

Starbear - Thank you for that clarification. I am looking at our QRH page IV, Immediate Action Section it states the following:
1. IF the Safe conduct of the flight is impacted:
a. AP.......................................................... .........OFF
b. FD.......................................................... .........OFF
c. A/THR......................................................... ....OFF
d. if below THR RED ALT .................................. pitch 15 / TOGA
if above THR RED ALT and below FL 100..........Pitch 10 / Climb
If above Thru RED ALT and abvoe FL 100.........Pitch 5 / Climb
Then there are conditions for flaps extended during approach.
Immediate actions complete go to page 72.

Page 72 leads to a series of tables. We fly all 319, 320, 321 so there are a lot of tables. These table have pitch and power settings for altitudes from FL 100 up to FL 400. Interpolation is required as the altitudes in the tables are FL 100, 200, 300, 350 and 400.

The original poster made this statement: In unreliable speed (all ADR's affected) you have to descend to FL250 to enable BUSS.

The only place where FL 250 is addressed in our QRH is at the latter end of the procedure and it has the following note:

If on an aircraft equipped with BUSS
When above FL 250
a. One ADR .........................................Keep on
b. TWO ADR pb's..................................Off

[this prevents the flight control laws from using two coherent but unreliable ADR data].

I believe that BUSS would still be available via one ADR above FL 250, from my reading of our QRH.

[Zaphod Beblebrox]

Vilas,

I am quite comfortable with our training and QRH. We teach the basics of pitch and power. The BUSS system is there in case there is an ADR, or air data failure and it will supply basic information. Using GPS and other inertial data the system is used to give a simple slow fast display output to keep the aircraft safe while the problem is dealt with.

I have flow both BUSS equipped A/C and non BUSS equipped and the basics are the same. Pitch and power. At altitude it's 3 degrees up and look up the power setting, which at mid weights is about 84%. Because our fleet is mixed we stress the pitch / power method because it always works. If there is a buss display fine but we still go to the charts.

I have never had a problem like this it the Airbuss but I have had an AirData failure on the B737-400. We ended up looking up power settings and using the FMC for support until we descended into warmer air. It was a curious fault, but actually a non event.

All this talk about airspeed and air data is because an Air France pilot and his partner locked the stick full back and rode a stalled airplane into the ocean. This kind of training is and should be done at the primary level. I have flow light aircraft with lost airspeed due to pitot icing. In the region of the great lakes where I trained it was possible to fly in complete clear VFR conditions at 3500ft. and then descend into clouds with light icing and a ceiling of about 1000 ft. It was a great way for a pilot to experience icing and an iced up pitot tube without undue danger.

[Lantirn]

BUSS is only available when all ADR's are off and it is irreversible.

I found it in the FCTM, the FL250 has to do only with the inflight experience that icing usually disappears during the descent to that level.

But although not documented, BUSS should be useable at all flight levels. (ADR 1+2+3 Fault ECAM)

[Starbear]

Zaphod are you sure your QRH does not tell you what to do below FL250 on BUSS a/c?

Extract from current A321 QRH Unreliable Airspeed:


AFFECTED ADR IDENTIFICATION
PROBE/WINDOW HEAT........................................................ ..............................ON
ALL SPEED INDICATIONS................................................. ......................X CHECK
ADR3 and STBY speeds use the data of the same probe.
􀁉 If at least one ADR is confirmed reliable:
RELIABLE AIR DATA........................................................ ........................... USE
UNRELIABLE ADR P/B(s)........................................................ .................... OFF
􀁉 If affected ADR(s) cannot be identified or all ADRs are affected:
􀁉 When above FL 250:
ONE ADR......................................................... ...............................KEEP ON
TWO ADR P/Bs.......................................................... ............................. OFF
This prevents the flight control laws from using two coherent but unreliable ADR data.
For flight continuation, Refer to Pitch/Thrust Tables.
􀁉 When below FL 250, if speed still unreliable:
ALL ADR P/Bs.......................................................... ............................... OFF
SPD......................................................... ........................... FLY THE GREEN
NAV ADR 1+2+3 FAULT Procedure................................................... APPLY


Extract from current A320/321 FCTM:


IN-SERVICE EXPERIENCE OF HIGH ALTITUDE PITOT OBSTRUCTIONS
Analysis of the in-service events shows that:
‐ The majority of unreliable speed events at low altitude are permanent situations, due to the
obstruction of pitot probes by rain, severe icing, or foreign objects (refer to the table above).
‐ At high altitude, typically above FL 250, the cases of unreliable speed situation are mostly a
temporary phenomenon: They are usually due to contamination of the pitots by water or ice,
in specific meteorological conditions. In-service experience shows that such a contamination
typically disappears after a few minutes, allowing to recover normal speed indications.

[vilas]

Zaphod Beblebrox
I believe that BUSS would still be available via one ADR above FL 250, from my reading of our QRHit don't say nuthin about descending to FL 250???These statements show that you are not sure about UAR procedure with the BUSS. There is a definite procedure how you go about it and when and how to get the BUSS. And you are not going to discover it by chance if it happens.
Lantirn, how do you know?
I know that the BUSS is valid below FL250 due to mach number effects in AOA vanes.

[Lantirn]

Villas,

Please check my previous post, I revised.
I was told by an instructor but now I assume (according triple ADR fault ECAM-no altitude limitation) that this is not correct about mach effects.

Feather44,

You have messed up BUSS availability together with unreliable speed procedure, ALL ADR OFF procedure (non BUSS aircraft) and ADR 1+2+3 Fault (BUSS equipped a/c only)

[vilas]

Not only you but a lot of people have said this about BUSS above 250 and I always wondered from where did they get this because there is not a word about this from airbus. The topic of BUSS, UAR and Triple ADR fail is generally spoken in same breath so FL250 has some how latched on to it. If a stall warning can work at high levels from AOA vanes then why not BUSS?

[Lantirn]

There is an association of FL250 and BUSS probably from the unreliable speed procedure.

I agree with you.

[donpizmeov]

When all three ADRs are switched off you go into direct law. Ever tried high altitude flight in direct law? This is non reversible. Leaving at least one ADR on allows ALTN law, and recovery of systems if/once Icing blockage clears.
Below 250 the thicker air make direct law flying much easier. It also allows time to get the aircraft sorted for the landing.

This is only for the unreliable airspeed case.

[vilas]

donpizmeov
Triple ADR fail doesn't put the aircraft in direct law but alternate law without protections. Refer DSC-27-20-20 P 2/8. There is some confusion about a particular MSN or SIM std. which puts the aircraft in direct law in clean configuration. This was discussed on another thread. Even the latest airbus briefing guide shows it in alternate law and recommends use of bird if available. A thought comes to mind that if at higher levels you suspect UAR you may be better off if by closing thrust levers and lowering attitude to -1degree attitude. Its MAY DAY any way. If it was due to freezing of Pitot in next five minutes you may be out of trouble.

[mcdhu]

..........or setting 1200kgs per side and 2.5 degrees NU will keep you safe at all levels.

mcdhu

[vilas]

..........or setting 1200kgs per side and 2.5 degrees NU will keep you safe at all levels.

mcdhuBut it may not solve the problem unless you descend below 250 that's where you should be in five minutes.

[donpizmeov]

The aeroplane does not know you can't read the airspeed. And continues to fly just fine unless you do something silly. Closing the levers and descending is great right up until you hit the ground.
In the 380 if you have unreliable airspeed and turn off all ADRs it will go into direct law. I haven't flown the mini bus so assumed they would be the same. My bad.

[donpizmeov]

An EY 346 lost airspeed in the cruise between Australia and the middle east some years ago. The pilots did the pilot thing, and maintained a safe flight path while sorting it out. It cleared after 5 min and they continued to AUH. The manufacturers checklist works..who would have guessed. You don't need to try and make up a new procedure.

[vilas]

It was just loud thinking not meant to replace official procedure which I am sure it works but some people have problem understanding the procedure. The incident you quoted any idea what's the cause and how did it clear after five minutes?

[donpizmeov]

Icing of probes. They had they same probes and mod state as the Air France A340.The procedure isn't very hard. Its just takes a little bit of time to read though and think about. In the old days we use to call it "Fly the aeroplane". Knowing the attitude and power for climb, cruise and descent etc is part of the job. You only need to look just behind the FDs to see it if not sure what they are.

[vilas]

That's what vaguely I was thinking. Instead of doing anything crazy 5mts. of descent would have saved 447.

[donpizmeov]

Letting go of the stick would have saved 447. So what are you going to do after descending 5 min. If you couldn't fly the aircraft before what happens in those magic 5 min? Divine intervention? You PA for a pilot on board?
This is not rocket science. Just learn how to fly the aircraft you are on. It's that simple.

One of the joys of flying a Bus is that for the most part it flies above the weather. If you ice probes you have hit a warmer air mass. Descending will keep you in Icing conditions delaying getting airspeed indication back, and will probably descend you into the weather and turbulence. This will greatly increase the workload. If a pilot can not handle loss of airspeed in a stable cruise situation, he will be very challenged now.
In aviation it's best to keep it simple. In the cruise if you loose the airspeed indication select the power and attitude you had prior to the loss. Run the checklist. Job done. If you want to get all fancy turn the bird on, but understand that attitude is what you need to fly, and bird will determine if you need more or less thrust.

[Lantirn]

donpizmeov,

The procedure is crystal clear:

-Xcheck indications, if one confirmed reliable, use that ADR

-If all sources are affected and above FL250, keep one on

-If all sources affected and below fl250, use the BUSS

There is not a word about immediately descending to FL250 to use the BUSS

[donpizmeov]

I was referring to Vilas who seems to like the descending bit.

[vilas]

I am not suggesting anything different. I was just thinking had 447 descended instead of doing what he did. I standby the official procedure. I have always supported manufacturer's procedures.

[vilas]

Lantirn
When you discover UAR will you keep AP on?

[Lantirn]

What do you mean?

Memo items, plus, there is a high probability that you will be in altn law

Edit: I think I know what you have headed for, the correct answer would be If the safety of the flight is impacted

[vilas]

My doubt is without AP can you continue in RVSM?

[Lantirn]

Ah, you meant after recovery.

Actually I never thought about RVSM it to be honest. Assuming that we had two correct remaining sources I would continue with AP on, yes, to be legal. Good hint.

[vilas]

No. Not after recovery. After discovery of UAR you disconnect AP and ATHR and fly pitch and thrust. All three ADRs are unreliable. Are you allowed to remain in RVSM?

[donpizmeov]

Procedure for unreliable airspeed is to turn all automatics off. That includes the auto-pilot. RVSM is a minor consideration. Fly the aeroplane. When safe to do so communicate with ATC.
I hope you don't teach this stuff vilas.

[Lantirn]

No. Not after recovery. After discovery of UAR you disconnect AP and ATHR and fly pitch and thrust. All three ADRs are unreliable. Are you allowed to remain in RVSM?

If all ADRs are unreliable you are in a serious emergency. No you are not allowed normally, BUT, if you declare mayday you don't care about separation and RVSM, it's the controllers job.

[vilas]

donpizmeov
I know the procedure including AP off. There is never any doubt about fly the plane. You did what you could you still don't have reliable ADR. My question is how long would you continue in RVSM air space in this condition? Especially your aircraft being in direct law. If there are no terrain issues would you not like to descend out of RVSM and take your chances? I am not suggesting anything but asking a question.

[donpizmeov]

I am not sure we are talking about the same thing. In the unreliable airspeed case above FL250, one ADR is kept on to keep you in ALTN law. I see no great rush to descend.