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Brand new Boeing unreliable airspeed procedure

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Brand new Boeing unreliable airspeed procedure

Old 25th Mar 2014, 17:44
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Brand new Boeing unreliable airspeed procedure

Hello to all of you,

Recently, Boeing has changed its Unreliable airspeed procedure, asking now as first items to take 4 pitch and 70% N1 while the normal parameters for cruize are around 25 and 85%.

Does somebody know the reasons which have motivated this strange change, most of all after the AF447 accident ?
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Old 25th Mar 2014, 17:55
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We airbus pilots would to welcome you to the group
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Old 26th Mar 2014, 00:46
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asking now as first items to take 4 pitch and 70% N1 while the normal parameters for cruize are around 25 and 85%.
Asking for those is asking for trouble.

What aeroplane are you claiming this applies to?
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Old 26th Mar 2014, 03:37
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The 777 didn't have an unreliable/airspeed checklist, the QRH only had a condition statement! Interesting that the 787 does have one.
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Old 26th Mar 2014, 04:01
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The 777 didn't have an unreliable/airspeed checklist
Eh? We've always had one! Just finished a Sim Phase in which we used it- a big take-away was that it didn't provide sufficient information for low level flight and approach- addressed with the current update.

HOWEVER- 4deg and 70% N1 as a memory item?

That DOES concern me.

It sounds lie a recipe for AF447 Mk2!!

Last edited by Wizofoz; 26th Mar 2014 at 04:43.
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Old 26th Mar 2014, 05:10
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It's for use when it's subtle and unobserved and it finally dawns on you that "it's bad" and you are already exploring the edge of the envelope but your instruments are apparently supplying confusing "valid" data.

It's simply a ball park figure to give you time to get the QRH out and find the (performance inflight) real figures! It's not a permanent fix! The plane may climb/descend/accelerate/slow down but it won't get out of control in the time it takes to as said find the real figures and use them.

Read some unreliable airspeed etc accident reports most are very subtle and the aircraft is either nose high low thrust because they "think" they are overspeeding or nose low high thrust as the "think" they are stalling, either case when you apply the "memory items" that will slow/stop the situation escalating in the wrong direction.

If it's a simple immediate loss of data, don't change pitch and power and go straight to the inflight perf as it's obvious.

Last edited by SMOC; 26th Mar 2014 at 05:49.
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Old 26th Mar 2014, 05:38
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It sounds lie a recipe for AF447 Mk2!!
Perhaps if they'd gone for 4deg and 70% things may have been different, seeing they spent most of the incident above 12deg.
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Old 26th Mar 2014, 05:44
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It's simply a ball park figure to give you time to get the QRH out and find the (performance inflight) real figures! It's not a permanent fix! The plane may climb/descend/accelerate/slow down but it won't get out if control in the time it takes to as said find the real figures and use them.
Come off the grass. Yes, it will climb (at over 1000ft/min) and it will slow down, a lot, in the time it takes to pull out the QRH. And yes, I suspect it'll go very close to going out of control (an Upset, at least) if you try 4/70% up high (as is indicated by the OP's "normal cruise"of 2.5/85%).

That's why I asked for some more details.
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Old 26th Mar 2014, 05:58
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Let's see... If already at cruise, why not Autothrottles OFF, retain last N1 setting, Autopilot to Altitude Hold?

70% N1 isn't going to keep a 747 at a reasonable airspeed at any reasonable cruise altitude, so it's a worthless "memory item"...
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Old 26th Mar 2014, 07:12
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Autopilot will most likely drop out. It will on the Airbus as the controls laws revert to Alternate. Manual flight it is until you exit the area and the probes clear. In the last few events it lasted only a couple of minutes.
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Old 26th Mar 2014, 08:34
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Clearly in the cruise, pitch and power are set and not changing and common sence would dictate not changing anything (ie maintain pitch and power).

It is for an unrecognised air data malfunction where the aircraft is now probably no longer at the correct pitch or power, cruise is probably the easiest one to spot it'll be the climb or descent where the A/P or F/D has gotten the aircraft in an excessively high or low nose attitude for the phase of flight chasing an unreliable speed for example.

757 crash "349kts" 15deg nose up, max thrust, and then reduced thrust to idle and pitched up to 18deg, by the A/P. It stalled.
727 crash 405kts climbing 6,500fpm FL230 Capt "no pull her back let her climb" stall warning / overspeed warning F/O there's Mach buffet, both agreed pull up, aircraft stalled descended 24,800' in 83 sec.
after a pilot's startled reflex reaction to an overspeed alarm sent an Air France Airbus A340-300 into a rapid climb, unnoticed by the crew.
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Old 26th Mar 2014, 10:20
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Wizofoz- It does now but there was a time when the 777 did not have an Unreliable checklist:

B777 checklists
The aircraft manufacturer provided checklists for UNRELIABLE AIRSPEED in
the quick reference handbooks (QRH) of its other aircraft types. Those procedures contained references to various indications that were available to the flight crew as evidence of unreliable airspeed. Examples of those indications included:
speed or altitude information not consistent with pitch attitude and thrust setting
airspeed/Mach failure flags
blank or fluctuating airspeed displays
variation between pilot in command and copilot airspeed displays
10 amber line through one or more primary flight display or Attitude Direction Indicator flight mode annunciations
overspeed indications
simultaneous overspeed and stall warnings.
The aircraft ADIRU was designed with system redundancy to prevent those
malfunctions from occurring, so no checklist such as UNRELIABLE AIRSPEED was provided for B777 flight crews. With only one erroneous input, the system was designed to automatically stop accepting that input and divert to another input source for information. That event would not require any action by the flight crew, and was intended to minimise the number of checklist items that a crew would need to action. With multiple erroneous sources of information or internal failures in the ADIRU, the EICAS message NAV AIR DATA SYS would be displayed. That
would direct the crew to the appropriate checklist and the unreliable airspeed table.
The nature of the accelerometer failure in this occurrence meant that the NAV AIR DATA SYS message was not displayed on the EICAS during the occurrence.
The B777 QRH Section 10 Flight Instruments18, displayed non-normal items. The checklists within the section related to messages displayed on the EICAS, and only consisted of condition statements. Those statements briefly described the condition which resulted in the respective EICAS messages, and did not contain procedural steps for the flight crew to action.
The AIRSPEED LOW status message, which was displayed on the EICAS at the start of the occurrence, was referred to in Section 15, Warning Systems, of the QRH, but required no crew response or action, as it was a condition statement.
The QRH preamble on non-normal checklist operation stated:
While every attempt is made to provide needed non-normal checklists, it is
not possible to develop checklists for all conceivable situations, especially
those involving multiple failures. In some unrelated multiple failure
situations, the flight crew may combine elements of more than one checklist or exercise judgement to determine the safest course of action. The captain must assess the situation and use good judgement to determine the safest course of action.
The only non-normal checklist available to the crew was the UPSET RECOVERY procedure which was specified in the non-normal manoeuvres section of the QRH.
This was from the ATSB report into the MAS 777 upset: 200503722.

So my statement is correct, the 777 didn't have an Unreliable Airspeed checklist, it does now.
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Old 26th Mar 2014, 11:06
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In the back of the Vol 3 of every Boeing I have flown there was a complete page of numbers for flight with unreliable airspeed, most of us would have had it copied, laminated and secured to our clip boards for quick and easy reference.
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Old 26th Mar 2014, 11:41
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So my statement is correct, the 777 didn't have an Unreliable Airspeed checklist, it does now..
Well, your statement also said "Interesting that the 787 does" which made it seem as if you thought the 777 STILL didn't.

But you're quite right, and instead of "Always" I should have said "For quite some time".
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Old 30th Mar 2014, 17:51
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The Airspeed Unreliable checklist is a new and improved Airspeed Unreliable checklist.
This check-list has been revised to account for recent accidents. There are pitch and thrust memory items for flaps extended and flaps up configuration. These values may not seem ideal for the B777 but they are identical for all Boeing models.
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Old 30th Mar 2014, 18:53
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There are no attitude or thrust targets in the NG QRH (very recently revised too). Simply "adjust attitude and thrust. Maintain airplane control" in the memory items and pitch/power tables.
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Old 1st Apr 2014, 09:22
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There is in the NG and its the same values. As said by sleeve of wizard they are identical for all Boeing models.

The numbers are a bit odd because of mixed fleet flying, but you'll won't crash. I'll try to find the Boeing wording.


PS: not agreeing with the new checklist, if you fly the thing you should know approx pitch & trhust settings.
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Old 1st Apr 2014, 09:42
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The following is some information, not all, from the Boeing symposium (can't find the document online). It talks about meetings between different manufacturers and how they will design their new unreliable airspeed checklists:

"...Procedures need to include memory items for initial pitch attitude and thrust setting:
• Settings need to maintain the airplane within the flight envelope until the checklist can be accessed
• Settings are valid at all weights and all altitudes
• Provide settings for Flaps Up and Flaps Extended
• Settings for climb with flaps are valid for all takeoff flap settings
• Settings should be standardized across all models as much as possible
• Do not change configuration while stabilizing the airplane with memorized settings
• If in a descent, stop the descent to accomplish the checklist...

....All models, all engine combinations, both heavy weight and light weight, high, medium and low altitudes, climb with all takeoff flap settings and flaps up cruise were analyzed. Best fit across all models was chosen to simplify the memory items....."

They then show a table of all Boeing models: the pitch is the same on all models, thrust varies:
Flaps up: 4 pitch, N1 between 75 and 90 %
Flaps extended: 10 pitch, N1 between 70 and 80 %
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Old 1st Apr 2014, 19:25
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Flaps extended: 10 pitch, N1 between 70 and 80 %
I wouldn't have thought that would be helpful in the landing config, given the normal pitch attitude is 0-1 and 60-70% N1 on the 777 and that's on a descending 3 glidepath. I haven't tried it out to see what happens but from inspection you'd get rather slow fairly quickly.

This seems to be taking "one size fits all" to extremes. Like rvblyky7 says, better to know a few more likely pitch/power settings or use what was working before the airspeed became unreliable.
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Old 2nd Apr 2014, 05:24
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Before issuing this new procedure, Boeing, their pilots, and their lawyers probably thought about this seriously.
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