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Using GPS ground speed to resolve Unreliable Airspeed

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Using GPS ground speed to resolve Unreliable Airspeed

Old 4th Jun 2019, 04:18
  #101 (permalink)  
 
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yanrair,

At one time in my career I also used to sit behind that 'green table' but mine was an old wooden desk. I had the same attitude as you about learning from experience and helping people in their jobs. The most important thing was to analyse what had happened and then publish what had been learnt. Some while ago I wrote a note on the slavish adherance to SOPs. I quote the final few paragraphs here:-

"However, despite all these considerations, it is impossible for the SOPs to cover every eventuality. There then comes the point when they are not appropriate to the situation and the captain decides to deviate from them. This is an extreme measure and should only be done when there is no other option and when the pilot has sufficient knowledge to understand fully the implications of what he is doing. I can think of several examples.

Suppose on take-off at maximum weight in a four engine aircraft (a 747 with multiple landing gears) at a hot and high airfield, birds are ingested into both engines on the same side. Then, when airborne only a few feet above the ground, and barely able to climb, the co-pilot calls positive rate of climb, but the captain elects to leave the gear down until more speed and altitude has been gained. Non-standard, but his reasoning is that the extra drag of the open doors and wheel wells will probably cause the aircraft to sink back towards the ground.

Suppose on final approach all engines suddenly stop. The captain elects to retract the flaps one notch. Non-standard, but the drag reduction is just sufficient to stretch the glide and make the airfield.

Suppose in mid-Atlantic, the underfloor cargo fire warning lights illuminate, the crew have reason to believe the warning is genuine and divert to the Azores. When they arrive the weather has deteriorated, the cross-wind has risen above limits and the cloud base has descended to below decision altitude. There is nowhere else to go and it is imperative to land. They do so successfully. All three examples were genuine events. It is not difficult to dream up other scenarios where such actions may be necessary.

And one more to ponder: the Qantas Airbus A380 at Singapore when a turbine disc exploded causing extensive damage and multiple unrelated warnings. In what order should the crew action the various procedures, which should be ignored and which have to be actioned?

My conclusion, therefore, is that normally flight crews should always obey the SOPs, even in an emergency, yet there may still be times when circumstances may dictate otherwise. Then, and only then, is it permissible and maybe essential to deviate, but this must be done in the full knowledge of ALL the implications. SOPs are for the guidance of wise men and not necessarily to be slavishly followed."


Not all flight managers act in the draconian manner that some posters here on PPRuNe seem to think!

Last edited by Bergerie1; 4th Jun 2019 at 04:55. Reason: grammar!!
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Old 4th Jun 2019, 08:58
  #102 (permalink)  
 
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Originally Posted by yanrair View Post
Dear Pineteam
Thats what I have been saying all along, with the addition of taking GS into account too. At the time of failure maintain status quo and if it was working a moment ago, it still will. And will continue to do so for a time. ...
GS extends your 1-2 minutes almost infinitely . Even if you don't know the wind ( which you will) In your scenario settle at 250 its GS with pitch and power accordingly. Unless you have a headwind or tailwind in excess of 50 kts you are perfectly safe. Your IAS must be in the range 200-300 which are both safe. Neither too fast nor too slow. And if the wind is stronger than that you will surely know about it and take it into account.

Y
Hi yanrair,

You need to include TAS effect with altitude.
In Pineteam's example of climbing away at 250 kts, climb thrust and 10 degrees of pitch works simply perfectly well. If you try to rely on Ground Speed and ignore wind component (when <50 kts) and TAS - then you will be in error by an additional 40 kts by 10,000 feet on the climb. (Your IAS must be in the range 160-260 kts - which is probably not safe).

KISS is the better solution.
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Old 4th Jun 2019, 10:55
  #103 (permalink)  
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Originally Posted by itsnotthatbloodyhard View Post


Sorry, this is not true. The A330/A340 FCOM has procedures for Unreliable Speed Indication, IAS Disagree, and All ADR Off - and NOWHERE does it make any mention of groundspeed. Nor does the FCTM.
I see this reply from a " BUS" pilot - you say there is no reference to GS and he says there is??
Would be good to know since I cannot imaging different Airbuss having different procedures??
Thanks for looking into it. All helps
Y

A bunch of AFCS systems revert to GS on approach in case of turbulence, even the bus. It's a fine reference for a minimum speed and the maths for wind correction isn't taxing. If you have nothing else then referring to GPS speed is an excellent idea and I've read it in more than one FCOM.

Here is what is says in my current QRH unreliable airspeed after pitch power initial items:
Quote:
d) Check all available data sources, including:

• FMS, POS - GNSS for ground speed,
• FMS, POS - GNSS INFORMATION for GNSS ALT (if required),
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Old 4th Jun 2019, 11:14
  #104 (permalink)  
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Originally Posted by Goldenrivett View Post
Hi yanrair,

You need to include TAS effect with altitude.
In Pineteam's example of climbing away at 250 kts, climb thrust and 10 degrees of pitch works simply perfectly well. If you try to rely on Ground Speed and ignore wind component (when <50 kts) and TAS - then you will be in error by an additional 40 kts by 10,000 feet on the climb. (Your IAS must be in the range 160-260 kts - which is probably not safe).

KISS is the better solution.
Hi Pineteam
It is simple at all altitudes - KISS I agree with.


The correlation between IAS and TAS/GS looks like this Ė 50 kts per 10,000 feet.

IAS G/S





Sea Level 260 260 /0

FL 100 260 310 /+50

FL 200 260 360 /+100

FL 300 260 410 /+150

Cruise Alt (350 ish) 260 460 /+200



How to use this? You only need to memorise the approximate G/S/ TAS for four flight levels and you have a guide which would have saved Air France. If they had only stayed at the current conditions of about 2 degrees of pitch,
80% N1 (or whatever cruise power was at the time) IVSI ZERO (works off IRS as well as pressure changes) ANDÖ. Kept the ground speed at 460 kts ( or whatever it was just after the failure) they would have had no difficulty in staying in full control. But they did not know this correlation.Or any correlation for that matter.

Here is a graph used in training in one airline...........









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Old 4th Jun 2019, 11:26
  #105 (permalink)  
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Originally Posted by Bergerie1 View Post
yanrair,

At one time in my career I also used to sit behind that 'green table' but mine was an old wooden desk. I had the same attitude as you about learning from experience and helping people in their jobs. The most important thing was to analyse what had happened and then publish what had been learnt. Some while ago I wrote a note on the slavish adherance to SOPs. I quote the final few paragraphs here:-

"However, despite all these considerations, it is impossible for the SOPs to cover every eventuality. There then comes the point when they are not appropriate to the situation and the captain decides to deviate from them. This is an extreme measure and should only be done when there is no other option and when the pilot has sufficient knowledge to understand fully the implications of what he is doing. I can think of several examples.

Suppose on take-off at maximum weight in a four engine aircraft (a 747 with multiple landing gears) at a hot and high airfield, birds are ingested into both engines on the same side. Then, when airborne only a few feet above the ground, and barely able to climb, the co-pilot calls positive rate of climb, but the captain elects to leave the gear down until more speed and altitude has been gained. Non-standard, but his reasoning is that the extra drag of the open doors and wheel wells will probably cause the aircraft to sink back towards the ground.

Suppose on final approach all engines suddenly stop. The captain elects to retract the flaps one notch. Non-standard, but the drag reduction is just sufficient to stretch the glide and make the airfield.

Suppose in mid-Atlantic, the underfloor cargo fire warning lights illuminate, the crew have reason to believe the warning is genuine and divert to the Azores. When they arrive the weather has deteriorated, the cross-wind has risen above limits and the cloud base has descended to below decision altitude. There is nowhere else to go and it is imperative to land. They do so successfully. All three examples were genuine events. It is not difficult to dream up other scenarios where such actions may be necessary.

And one more to ponder: the Qantas Airbus A380 at Singapore when a turbine disc exploded causing extensive damage and multiple unrelated warnings. In what order should the crew action the various procedures, which should be ignored and which have to be actioned?

My conclusion, therefore, is that normally flight crews should always obey the SOPs, even in an emergency, yet there may still be times when circumstances may dictate otherwise. Then, and only then, is it permissible and maybe essential to deviate, but this must be done in the full knowledge of ALL the implications. SOPs are for the guidance of wise men and not necessarily to be slavishly followed."


Not all flight managers act in the draconian manner that some posters here on PPRuNe seem to think!
Dear Bergerie
Looks like we went the same college of airmanship.
I could add many more to that list - a lot of folk think that every time the manufacturer must have thought out a solution and it is in the good book. But no. Boeing make great planes but I always used to say, "they don't know how to fly them in an airline environment." And they don't even try. A Boeing FCOM 1 (user handbook if you own a washing machine) barely scratches the surface of how to operate an airliner.
Take 767 engine fail at 30W mid Atlantic. QRH says descend to drift down altitude. (FL 330) and set up MCT. It happened to one of my guys. He did nothing of the sort , arguing that that to sit there at MCT on the remaining engine was inviting a second failure. So, he descended to FL 200 and flew along at a nice low power setting - way below MCT to Gander where he landed with no drama and without having gunned his remaining engine for 2 and a half hours. Why do Boeing not say this? For the reason that you state - it is beyond the scope of the QRH and of course you might, just might need that extra altitude to give you extra range if your diversion field is at ultimate distance. But with Gander so close this didn't matter. And so airmanship kicked in. Funny old archaic thing that used to be prevalent.
Y
Cheers
John
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Old 4th Jun 2019, 12:22
  #106 (permalink)  

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Dear John.

You keep missing the point where AF447 crew failed to maintain the normal pitch of 1-2.5, deg and a hefty dose of thrust (makes no difference if 80 or 95 N1), failed to do nothing just keep the ESSENTIAL two parameters the same. Giving them an Excel graph, forcing to memorize it, would greatly help them - I think not. Quite on par with the act where you could not add up HW and TW correctly, and thus the precision GS method to reach IAS = Vref = 100 at touchdown would put your followers into a stall with IAS of 60 kts at 2500 ft.

If the traits you claim to have are true, surely you see that a method which has its proponent fail to calculate correctly, (let alone explain it over a few days), from the comfy space in front of a computer screen, is of absolutely no use to a crew in distress.

Leading Airman worth their salt understand that if a crew fails to execute a procedure the solutions are: (any combination of)
- focus the syllabus, enabling a better understanding of priorities
- raise the fail/pass standard, enforcing a better drill
- simplify the underlying procedure

Adding overlay mumbo-jumbo procedures only makes things worse for the next unfortunate lot. Severely worse as a matter of fact.
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Old 4th Jun 2019, 17:04
  #107 (permalink)  
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Originally Posted by Bergerie1 View Post
yanrair,

My conclusion, therefore, is that normally flight crews should always obey the SOPs, even in an emergency, yet there may still be times when circumstances may dictate otherwise. Then, and only then, is it permissible and maybe essential to deviate, but this must be done in the full knowledge of ALL the implications. SOPs are for the guidance of wise men and not necessarily to be slavishly followed."

Not all flight managers act in the draconian manner that some posters here on PPRuNe seem to think!
Complex situations that exceed the boundaries of SOP's and NNCL's/QRH/FCOM procedures happen. When the books are placed in the corner and the crew have to roll up their sleeves and deal with the real world, the value of the procedures that are now not necessarily being followed still exists; the very fact that the crew are electing to deviate means that there is a change in conditions outside of normal. If that is a result of error, or stress, interruption or other cause, the fact that what is happening is different is highlighted and that is a trigger for crew to contemplate. The vast majority of events that occur remain within the guidelines of the procedures that have been developed. Occasionally they go way outside. The stress of malfunctions is exacerbated by control difficulties, or where the warning systems are swamped by cascading alerts. The handling stuff goes back into the past, there may be a bit of wishful thinking about better performance in the old days, there were many examples of tragic loss of flight control in the past, not so dissimilar to the most recent events. One concern in many of the events is that getting out of sorts, many events have data showing full back stick being applied contrary to a rational recovery from the loss of control condition. That includes 1st world top flight programs as well as other operations with less stellar reputations. Not too many aircraft will survive a continuous back stick input (notwithstanding the MCAS saga's) in a stall or departure. When the data shows roll rates over 180 degrees a second on a Part 25 aircraft, there is a hint that not all was well in the handling dept. Point is, humans in stressful situations have a wide range of performance outcomes in dealing with the issues confronting them. The industry had the sober lesson of SR111, which showed that disciplined methodical process may not always be the best option.

With the level of operation, I would think that the industry overall doesn't do a bad job dealing with abnormal conditions; for the number of events that occur every day the wild rides while distressing are not a great rate of occurrence, the problem is the consequential impact to the individuals concerned.

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Old 5th Jun 2019, 16:49
  #108 (permalink)  
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Originally Posted by FlightDetent View Post
Dear John.

You keep missing the point where AF447 crew failed to maintain the normal pitch of 1-2.5, deg and a hefty dose of thrust (makes no difference if 80 or 95 N1), failed to do nothing just keep the ESSENTIAL two parameters the same. Giving them an Excel graph, forcing to memorize it, would greatly help them - I think not. Quite on par with the act where you could not add up HW and TW correctly, and thus the precision GS method to reach IAS = Vref = 100 at touchdown would put your followers into a stall with IAS of 60 kts at 2500 ft.

If the traits you claim to have are true, surely you see that a method which has its proponent fail to calculate correctly, (let alone explain it over a few days), from the comfy space in front of a computer screen, is of absolutely no use to a crew in distress.
Adding overlay mumbo-jumbo procedures only makes things worse for the next unfortunate lot. Severely worse as a matter of fact.
Dear Flight Detent
You have referred before to my appalling mathematical ability when in bed using an iPhone to respond to these forums, which I have admitted to. Mea Cupla. I give in. Indeed since then I have now resorted to responding wide awake and in front of my large screen with a keyboard. Like now.
And I have pointed out that on a real flight deck with real instruments in front of me, failed or otherwise, I would not have any trouble sorting out wheat from chaff. It is not so easy when trying to picture HW/TW etc and putting it down on paper remotely in a theoretical setting. But now armed with paper and pencil, I will try again.
And in your QUOTE above you don't memorise the graph. It is carried at hand for reference and can be used in seconds. But you do memorise the 50 its per 10,000 feet increase in TAS with altitude, which isn't too hard because I can do it.

First I must object to you repeatedly using my maths errors in a previous post, which I have since corrected, to suggest that the use of GS in UAS is a not worthy of consideration. Either it is a good idea or it is not, and Boeing have it in Line 4 of the QRH for UAS. What I am trying to get going here is a discussion about HOW it might be used effectively, which it most certainly can. I know that from training if you ask a pilot what line 4 in the QRH means, you get some very divergent answers! And that is not good at all , at all, as they say in my part of the world.
BOEING QRH 737-400 Line 4. CROSS CHECK IRS AND FMC GS AND WINDS TO DETERMINE AIRSPEED ACCURACY...................

If I had suggested the world was round and not flat, but made an error in part of the discussion, using your logic, you can reject the entire argument on the basis of an error in one part. Tackle the ball - not the man.
From various replies here you can see that many pilots do indeed find GS useful and I find it more than useful. So do Boeing. Otherwise it wouldn't be in the QRH.
It is useful all the time and particularly on the approach when GS +/- the wind is more or less the same as IAS, so it is absolutely accurate in that situation. Likewise after takeoff. On one or two previous types we flew the approach using a minimum GS, and the Airbus does it automatically using GS mini, I think it is called. But let's not go there.
At altitiude there is a very simple table which I know you don't like, which resolves the issue of not being at MSL.
On a point here, have you ever actually done any of this for real? It sounds to me as if you haven't. I have flown using GS alone umpteen times in the sim. in all sorts of situations (was trained this way on the 737-200 which had doppler GS before GPS) and it transforms what was always a difficult exercise into something entirely manageable.
And as someone else has pointed out. PITCH/ POWER tables are set for a particular airspeed and configuration, and if you set the pitch and power while at a totally different speed, it won't work. GS sorts this out for you.
Example. 737-400 from QRH tables Straight and level flight at 52 tonnes 737-400. 210 knots is 6 deg NU and 60% N1. The "six and sixty rule known by most 737 guys I know).

Now, if you are at 340 knots that won't work and you will be in a climb of about 2000 fpm with rapidly decreasing airspeed and very confused indeed.
I am really trying to engage politely here in what is a very serious matter and I hope we can continue the discussion calmly and tackle the core issues of how are we going to fly our plane in wide range of situations using the GS as a reference as given to us in the QRH.
Over, but not out, yet!! Off to see my therapist now...........
Cheers
Y


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Old 5th Jun 2019, 17:10
  #109 (permalink)  
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POST 103 FROM Bergerie
And one more to ponder: the Qantas Airbus A380 at Singapore when a turbine disc exploded causing extensive damage and multiple unrelated warnings. In what order should the crew action the various procedures, which should be ignored and which have to be actioned?

Bergerie
This warrants its own thread I think since in some ways it is the root of everything we are discussing here. QF had 64 (I think) different failures. Safe landing a long time later. Amazing bunch of highly qualified guys on the flight deck including an expert on systems. No fire.
1968. GARWE BOAC 707 takes off from LHR with severe engine failure and fire. A bit like Concorde. Back on ground in something like 5 minutes. Plane burned out but many survived. All would have died if captain had started doing "procedures". He knew the plane would not survive too long and landed.
Interesting isn't it and worthy of discussion perhaps elsewhere?
Y
https://en.wikipedia.org/wiki/BOAC_Flight_712
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Old 5th Jun 2019, 20:41
  #110 (permalink)  
 
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Originally Posted by yanrair View Post
.......
1968. GARWE BOAC 707 takes off from LHR with severe engine failure and fire. A bit like Concorde. Back on ground in something like 5 minutes. Plane burned out but many survived. All would have died if captain had started doing "procedures". He knew the plane would not survive too long and landed.
Interesting isn't it and worthy of discussion perhaps elsewhere?
https://en.wikipedia.org/wiki/BOAC_Flight_712
Hi yanrair,
If only the Fire Control Handle had been pulled on No 2 engine during the Engine Fire Check List, then the LP fuel valve would have closed and there would not have been a fuel fire in the Pylon.
see page 20 of https://www.era.lib.ed.ac.uk/bitstre...=1&isAllowed=y
Then perhaps Capt. Taylor would not have had to demonstrate such exceptional skill and judgement.
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Old 5th Jun 2019, 22:45
  #111 (permalink)  
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Originally Posted by Goldenrivett View Post
Hi yanrair,
If only the Fire Control Handle had been pulled on No 2 engine during the Engine Fire Check List, then the LP fuel valve would have closed and there would not have been a fuel fire in the Pylon.
see page 20 of https://www.era.lib.ed.ac.uk/bitstre...=1&isAllowed=y
Then perhaps Capt. Taylor would not have had to demonstrate such exceptional skill and judgement.
Yes indeed Goldenrivett!
Thats what happened though like Papa India, the design was poor. It allowed you to fire the bottles without having fully pulled the fire handle. My memory is that it was partly pulled. As we know on later models you have to twist the fire handle positively to arm the bottles and it is all annunciated with warning lights.
ďA superior pilot is one who exercises superior knowledge to avoid using his superior skillĒ. Always true. But having found they had an engine fire out of control the point is he got it on the deck in 4 minutes. That sort of thinking isnít taught today.
i have seen airline crews in sim. with severe engine failure- ok no uncontrolled fire, take 50íminutes to complete the checklists. Thatís a long time with an engine that exploded!

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Old 6th Jun 2019, 09:11
  #112 (permalink)  
 
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Originally Posted by yanrair View Post
Thats what happened though like Papa India, the design was poor. It allowed you to fire the bottles without having fully pulled the fire handle. My memory is that it was partly pulled.

According to the accident report - the handle was never pulled. See Page 20.
"On this occasion the difference between the two drills, was in advertently obscured by the Flight Engineer, who went for, but did not pull, the fire shut-off handle whilst carrying out the Engine Overheat or Failure Drill; it appears that this not only gave him the impression that he had pulled the fire shut-off handle as part of the fire drill, but also gave the same impression to the First Officer."

BOAC had 2 similar procedures then - with the vital difference of pulling or not pulling the FCH. The crew started one procedure - then changed when they realised the fire warning. They thought the handle had been pulled - but actually it had not.
Later the two procedures were were amalgamated into one - to make it simpler.

KISS principal again.
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Old 6th Jun 2019, 12:06
  #113 (permalink)  

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Originally Posted by yanrair View Post
No twist. Stabilize plane setting sensible pitch power for conditions. You are now safe. Then refer to GS to ENSURE that your previous setting have achieved a safe airspeed and keep it there.
y
It is upside down indeed. They ask you to use gps ALTITUDE which on the Bus is accurate within 100 ft

Last edited by FlightDetent; 6th Jun 2019 at 13:23.
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Old 6th Jun 2019, 12:47
  #114 (permalink)  

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Yanr, let's get this straight. Two key points will be enough.
Originally Posted by yanrair View Post
First I must object to you repeatedly using my maths errors in a previous post, which I have since corrected, to suggest that the use of GS in UAS is a not worthy of consideration.
A) Stop twisting.
1) I had not used your math errors before, ever. Even in the post you have in mind, and that was only once, I used the CORRECTED math, which is the one that would have put the crew into a stall at Vref-40 kt.
2) I did not suggest GS was not worthy of consideration in UAS. Au contraire, post #47 "This thread inspires me to include GS in that scan the next time."

B) Heed your own advice
Tackle the ball - not the man.

...you do memorise the .... which isn't too hard because I can do it. ...
...On a point here, have you ever actually done any of this for real? It sounds to me as if you haven't. ...
... you can reject the entire argument on the basis of an error in one part ....
... very simple table which I know you don't like ....

... Off to see my therapist now...
--- now, if we can play neat ---

About the GS uses i.a.w. present OEM guidance:

you decided to quote
BOEING QRH 737-400 Line 4. CROSSCHECK IRS AND FMC GS AND WINDS TO DETERMINE AIRSPEED ACCURACY...................
It does not say "to determine airspeed accurately" as in: and then fly the GS, which is what you seem to propose through the previous posts.

The full version from my copy (click here): says below the dashed line
4. Cross check the IRS and FMC ground speed and winds to determine airspeed accuracy if indicated airspeed is questionable.
-> To me that reads: try with GS to figure out if any of the ASI can be trusted and the scale of the error at hand. No mention of flying anything through GS.

The Airbus instructions are somewhat different, (click here for the basic scheme).

- The last element in FCTM wording: "Flight using pitch/thrust references or the BackUp Speed Scale (BUSS, below FL 250), if the troubleshooting has not enabled to isolate the faulty ADR(s)." has almost a full page of explanations. No GPS reference at all.

- The "Troubleshooting and Isolation" does not mention GPS or GS at all, again. Though in cruise I personally would. Looking at the CoFP and comparing the printed GS against the present display readout, keeping in mind the difference between the two observed previously.

- The "Flight path stabilization" is where they acknowledge use for GPS altitude. As a suggestion, after what is already 20 lines of text in that paragraph on how to fly stabilized.
The GPS altitude can be used to confirm that the aircraft is maintaining level flight.

Originally Posted by yanrair
...how are we going to fly our plane in wide range of situations using the GS as a reference as given to us in the QRH.
There no reference to do that in the 737 QRH. There is whatsoever no reference to GPS GS in any of the UAS / ADR / Disagree procedures on A320/A330, FCOM, QRH, FCTM and memory items included.

I have no issues with your graph, which is correct and valid. The observation was: For the sorry AF447 crew who that night did not have the ken to maintain the cruise pitch and not touch the thrust-levers, memorizing certain datapoints of it (50 kt/ 10k ft) would not have helped.
Later, when fully stalled and perplexed due to the confusing indications both active and missing, the meaning of 60 kt-ish GS could have lit a spark that could have saved them all, definitely yes - but even for that the TAS table is absolutely irrelevant.

I do opine, OTOH, that the claim of flying accurate speed under UAS using a GS readout is bogus. The present procedures - which do not include any GS at all - give good enough result within 10 knots already as they are. Attempt to finetune that with GS would most likely unsettle the whole process, given the dynamic nature of the atmosphere itself. Very different outside compared to the SIM one.

Pass my greetings.

Last edited by FlightDetent; 6th Jun 2019 at 13:40.
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Old 6th Jun 2019, 20:59
  #115 (permalink)  
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Originally Posted by Goldenrivett View Post
According to the accident report - the handle was never pulled. See Page 20.
"On this occasion the difference between the two drills, was in advertently obscured by the Flight Engineer, who went for, but did not pull, the fire shut-off handle whilst carrying out the Engine Overheat or Failure Drill; it appears that this not only gave him the impression that he had pulled the fire shut-off handle as part of the fire drill, but also gave the same impression to the First Officer."

BOAC had 2 similar procedures then - with the vital difference of pulling or not pulling the FCH. The crew started one procedure - then changed when they realised the fire warning. They thought the handle had been pulled - but actually it had not.
Later the two procedures were were amalgamated into one - to make it simpler.

KISS principal again.
apolgies I think we are into thread creep territory?
Yes thatís true. The engineer thought he had but hadnít. The point is that you could fire the bottles without having pulled the fire handle which masked the error. On a 737 for example that canít happen Anyway it was not done correctly I agree. What happened next is what Iím saying is almost unthinkable today- to land in four minutes. 4 passengers died. Plane totally burned out in a very short time. All you need to land is the wheels. Nothing else. No speeds weights or dumping needed -180 will do on long runway. And thatís pretty much what they did.
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Old 7th Jun 2019, 04:46
  #116 (permalink)  
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Originally Posted by yanrair View Post

apolgies I think we are into thread creep territory?
Yes thatís true. The engineer thought he had but hadnít. The point is that you could fire the bottles without having pulled the fire handle which masked the error. On a 737 for example that canít happen Anyway it was not done correctly I agree. What happened next is what Iím saying is almost unthinkable today- to land in four minutes. 4 passengers died. Plane totally burned out in a very short time. All you need to land is the wheels. Nothing else. No FMC Entries , speeds weights or dumping needed -180 kts will do on long runway. And thatís pretty much what they did.
The BOAC logic was that for simple engine failure with no fire you didnít need to pull fire handle. After ďWEĒ they changed to ďalways pull fire handleĒ - you can always push it / twist it back again. Y
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Old 7th Jun 2019, 09:45
  #117 (permalink)  
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Reply to thread 116
quote. I used the CORRECTED math, which is the one that would have put the crew into a stall at Vref-40 kt.

So again we are saying that using GS can be proven unworkable because of something I wrote earlier. I have reworked the argument since then without, I think, mistakes and it the basic premise that GS is a tool that is much misunderstood in its usefulness (or otherwise of course) which should be addressed.
If I were to prove that the world is round in a dissertation and accidentally suggested that the earth is 93,00,000 miles from the sun and has a circumference of 24 000 km, then some using this logic, might suggest that world might be flat. Because I made an error(s). But despite those errors the earth is still round, unless of course one belongs to that society in London.
So to the key points
We all accept now, and we did not at the start, except some still calling GS "bogus" , that GS has its uses and everyone seems to agree that where you have Airspeed Disagree, GS is great for sorting out which of three ASIs is the functioning one. Transfer control to other pilot. Continue drinking tea which didn't even spill. That's the easy one but even that I have seen screwed up into a nightmare if badly handled.

Now, a dark and dirty night with all three ASIs frozen at differing speeds, and perhaps overspeed warnings coupled with underspeed and possibly stick shakers. AP has disconnected. First Officer continued to follow Flight Directors for a while which has messed up the pitch and power. So you are there with almost no valid information and I bet very frightened.
The only source now is a set of tables in the QRH which must be accessed and the correct set extracted from many different configurations - and of course our first officer is not familiar with these tables having only seen then during training. And the tables only work if you at the flight level, weight and configuration stated AND the SPEED stated. if during the upset just related, the speed has gone elsewhere (AF447 and ET being examples where the speed was a couple of hundred knots away from the condition that pre-existed, they are of no use at all.
To the rescue our GS whereby I just fly the GS that I see now, or return it to where it was.
In this situation I would simply set my approx. Pitch Power depending on Flight Level ,which knowledge no pilot should be without, and maintain my safe groundspeed which existed at the time of the failure. Or as stated on the flight plan. Or what I remember it to be. Thats it, safe and a long way from either stall or overspeed.
Taking an easy one. I have this problem after takeoff clean. Maybe FL 50 climbing. Set "six and sixty" and 250 GS. And level off. Don't accelerate or decelerate. Calm restored. Now consult QRH which says for 52 tonnes, 240 knots, 6 deg pitch and 64% N1 (data from 737-400 QRH date 2010 ). Set 65% and monitor GS so that it stays around 250 kts. Can adjust for wind of course. Return to land using pitch and power but keeping the speed in the band quoted in the tables using GS all the way down.
I think that is the briefest explanation I can offer without the A level maths.
And I have done it umpteen times and it works.
Safe flying.
y

Y
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Old 7th Jun 2019, 10:23
  #118 (permalink)  
 
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I do opine, OTOH, that the claim of flying accurate speed under UAS using a GS readout is bogus. The present procedures - which do not include any GS at all - give good enough result within 10 knots already as they are.
I'll weigh back in here. I don't think anybody is claiming that GS will give you an "accurate" speed, depending on how it is defined. But what stands out like dog's balls to me is that if GPS GS was used in these two scenarios, the speed could have been actively controlled/limited to enable continual overriding of the MCAS at a mid-speed instead of Vmo.

From an old 737 FCOM, the 70 tonne flap Up holding power is only 66% N1. The UAS is what, 75%? Even with a slight climb (UAS Memory Items) the speed is going to start increasing, and as the speed increases, the drag reduces and the acceleration increases. The Ethiopians were dead in 5 minutes, commencing the last dive at Vmo. Do you lot really think that, with all that was going on, pulling out the QRH and going through the tables while maintaining the UAS memory Items was actually going to work? The Lion Air guys had the QRH out, apparently. They were flying for 11 minutes and still dived into the ocean at warp speed. The GPS GS would have told them all they needed to know about the speed. Ignore it at your peril.

Last edited by Capn Bloggs; 8th Jun 2019 at 10:35. Reason: clearing up some typos
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