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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 29th May 2019, 23:09
  #61 (permalink)  
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Originally Posted by iceman50 View Post
Capn Bloggs
Why did you not quote the full Airbus Procedure as what you quoted would be after the stabilization of the aircraft. You can twist anything to make a point!
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
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Old 29th May 2019, 23:22
  #62 (permalink)  
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You are not going to get a gps jam just as your birds or ice or whatever it is disables your air data systems. Not going to happen.
Its a cinch
TAS INCREASES BY 50 kt per 10000. So if the following are at a safe speed at MSL you have all you need is this knowledge

MSL
250:kts IAS AND GS
FL 100. 250 kts IAS= 300 GS
FL200 250 IAS = 350:GS
etc etc
At FL350 250:kts IAS = 450 kts.

If you fly these GS in still Air you are safe. OK - then +/- the wind which is elementary maths.
You could fly a whole flight from takeoff to landing using this info and always have safe margins.
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Old 30th May 2019, 03:13
  #63 (permalink)  
 
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Originally Posted by Iceman
Why did you not quote the full Airbus Procedure as what you quoted would be after the stabilization of the aircraft. You can twist anything to make a point!
Cool it, Ice. I never claimed you do that GPS stuff BEFORE the memory items. I merely pointed to evidence that suggests that RAD ALT ALIVE's assertion that GPS isn't mentioned in any manuals appears to be rubbish. Even more concerning is that they appear to be an Airbus driver.

In any case, any reader is quite welcome to click on the link I provided (I even gave the page number, for goodness sake) to see what I was getting at.

Anyway, fly any way you like. I (and YT! ) will be calling Pineteam's tower for the 3000ft wind and cruising down final looking closely at the GPS speed. A "Reference Groundspeed Approach" I believe they used to call it!
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Old 30th May 2019, 04:20
  #64 (permalink)  
 
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Originally Posted by yanrair View Post


Perfect.
2500 ft tailwind 20
airfiel wind headwind 20
So your landing GS will be 20 kts less than V Ref. Say VRef 100, then fly whole approach at 120 GS. Your IAS will be 140 at 2500 and 100 on landing. Just what you were looking for- no? A perfect touchdown speed. Not approx.
more commonly one has reducing headwind during final descent. Say 30 kts HW at 1000 ,and 5 kts at touchdown. VRef 100.
Fly whole approach at 105 kts. GS. You will land at EXACTLY 100 VRef!
this is precision flying- not guesswork. Clearly you use manufacturer Pitch/power tables too to give you a clue but then refine the outcome using GS.
Hello Yanrair,

I did not say the wind was 20 kt headwind on ground lol. It usually goes from a strong tailwind around 2500 feet to a crosswind/ light headwind. Anyway I don't deny you should not use the GS as a tool. If you are 200kt GS on short final, something is wrong. But I think it's safer to keep it simple. Pitch and Thrust is all you need to fly safely to the ground. A quick look at the GPS can help but should not be relied on. If for some reasons I have Unreliable airspeed on final, I know with 4 degree pitch and 50% N1 with F3 and gears down on A320 I'm safe. No need to do maths in a critical phase of flight and that's how Airbus expect you to fly in that case according to the QRH. =)
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Old 30th May 2019, 07:40
  #65 (permalink)  
 
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I have watched this discussion with great interest. Most inputs have been from pilots who have never flown using AoA. I detect the odd Ex Military pilot who supports the use of AoA rather than the ridiculous suggestion of using GS as a substitute for IAS.

I have flown for nearly 40 years using AoA as a primary means to control my aircraft. Although IAS was used throughout, it was totally possible (and practised) to fly and land using AoA, power settings and attitude (aircraft not pilots)!

AoA should be displayed in ALL aircraft and its use and relevance taught from initial pilot training right through to a Line Check or Combat Ready.
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Old 30th May 2019, 08:36
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Want a great example of an A330 with unreliable to no airspeed, and use of ground speed as a source of information?

Youtube ‘Malaysian unreliable airspeed’ ...a Malaysian A330 that departed YBBN with the pitot covers still on.
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Old 30th May 2019, 10:05
  #67 (permalink)  
 
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Originally Posted by yanrair View Post


Perfect.
2500 ft tailwind 20
airfiel wind headwind 20
So your landing GS will be 20 kts less than V Ref. Say VRef 100, then fly whole approach at 120 GS. Your IAS will be 140 at 2500 and 100 on landing. Just what you were looking for- no? A perfect touchdown speed. Not approx.


You are dangerously in error. You say you are flying 120 GS on the whole approach. There is a 20kt tailwind at the top and 20kt headwind at the bottom. That means your IAS will be 100KIAS at the top and 140 at the bottom. Great job shooting your own method in the foot with such a convincing demonstration of how easy it is to get wrong. Good news is you get to practice a stall recovery and a touch and go in one approach.

Last edited by oggers; 30th May 2019 at 10:20.
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Old 30th May 2019, 12:56
  #68 (permalink)  
 
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Originally Posted by we_were_inverted View Post
Want a great example of an A330 with unreliable to no airspeed, and use of ground speed as a source of information?

Youtube ‘Malaysian unreliable airspeed’ ...a Malaysian A330 that departed YBBN with the pitot covers still on.
Except it was using AoA. From the ATSB report: “In accordance with published procedures, the flight crew turned off the three air data reference systems (ADRs) at 1343. This activated the aircraft’s backup speed scale (BUSS) (Figure 3), which provided a colour-coded speed scale derived from angle of attack” [my bold].

I’m with Dominator2 - give me AoA any day.
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Old 30th May 2019, 22:41
  #69 (permalink)  
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Originally Posted by Capn Bloggs View Post
Cool it, Ice. I never claimed you do that GPS stuff BEFORE the memory items. I merely pointed to evidence that suggests that RAD ALT ALIVE's assertion that GPS isn't mentioned in any manuals appears to be rubbish. Even more concerning is that they appear to be an Airbus driver.

In any case, any reader is quite welcome to click on the link I provided (I even gave the page number, for goodness sake) to see what I was getting at.

Anyway, fly any way you like. I (and YT! ) will be calling Pineteam's tower for the 3000ft wind and cruising down final looking closely at the GPS speed. A "Reference Groundspeed Approach" I believe they used to call it!
On TristaR we used iT a lot in wind gradient conditions. Remember landing LHR 23 with surface wind 210/45 and 2000 ft wind 210/70. So we would lose 25;kts during approach. VRef+5 was 140. So flew whole approach at 115 kts GS. NEVER TOUCHED POWER ALL THECWAY DOWN DUE STABILITY OF APPROACH.
Y
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Old 30th May 2019, 23:14
  #70 (permalink)  
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Originally Posted by oggers View Post
You are dangerously in error. You say you are flying 120 GS on the whole approach. There is a 20kt tailwind at the top and 20kt headwind at the bottom. That means your IAS will be 100KIAS at the top and 140 at the bottom. Great job shooting your own method in the foot with such a convincing demonstration of how easy it is to get wrong. Good news is you get to practice a stall recovery and a touch and go in one approach.
You are right buddy. It was late and i screwed up on simple math but actually there was no stall since IAS was safe in spite of incorrect math. But no matter. The principle is flawless despite my maths in the above being pre-primary level!
should have said fly approach at GS 80 = IAS 100
downwind maybe fly GS 140=IAS 120
point is it works.
Now someone mentioned pitch /power which is paramount as a starting point. Agreed 737 it’s 6pitch/60N1
But do need your weight too.
Amd on the approach your pitch power change due to headwinds. But you don’t know by how much do you !
GS solves this
y
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Old 30th May 2019, 23:17
  #71 (permalink)  
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Originally Posted by scifi View Post
It seems as if we are assuming we don't know the actual windspeed, when this can be found by asking the nearest ATC unit for their ground windspeed, then adding the correction of twice that and add 30 degrees to find the wind velocity above 1000 ft.
.
OurvGS always works so no need for ATC and maths.
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Old 1st Jun 2019, 22:05
  #72 (permalink)  
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The simple fact is that GS can be used in every phase of flight to back up pretty accurately PITCH POWER/WEIGHT /ALTITUDE TABLES provided by OEM.
It is possible to fly completely safely an entire flight just by reference to ground speed using two things
WIND
TAS INCREASE WITH ALTITUDE = 50kts/1000 ft
thats it.
And if you are caught in a sudden chaotic UAS + SHAKER + MULTIPLE WARNING just maintain current GS PITCH AND POWER.
if anyone thinks this doesn’t work get yourself on a sim. Right away. It does.
Safe flying
Y
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Old 2nd Jun 2019, 00:39
  #73 (permalink)  
 
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Originally Posted by yanrair View Post
It is possible to fly completely safely an entire flight just by reference to ground speed using two things
WIND
TAS INCREASE WITH ALTITUDE = 50kts/1000 ft
You’re sure about that?
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Old 2nd Jun 2019, 03:15
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[QUOTE][ou are not going to get a gps jam just as your birds or ice or whatever it is disables your air data systems. Not going to happen.
Its a cinch
TAS INCREASES BY 50 kt per 10000. So if the following are at a safe speed at MSL you have all you need is this knowledge
/QUOTE]
is the quote I think.
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Old 2nd Jun 2019, 04:15
  #75 (permalink)  
 
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Yanrair, if it was a good idea to use GPS in an unreliable airspeed case, aircraft manufacturers would recommend using it.
Read your previous post again: 2 serious mistakes that in real life will put you in a dangerous situation. Don’t try to reinvent the wheel.
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Old 2nd Jun 2019, 07:47
  #76 (permalink)  
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Originally Posted by pineteam View Post
Yanrair, if it was a good idea to use GPS in an unreliable airspeed case, aircraft manufacturers would recommend using it.
Read your previous post again: 2 serious mistakes that in real life will put you in a dangerous situation. Don’t try to reinvent the wheel.
Some airlines do use GPS in UAS training.
OEM plane makers generally don’t teach airlines how to operate in difficult situations. In my last major airline a great deal of the training was developed locally
the fact that I made a typo in a previous post that was glaringly obviously a typo does not alter the fact that GS is a pretty foolproof way of avoiding calamity in serious confusing UAS situations with multiple distractions. Over years I have seen pilots flying calmly through situations which, if you don’t believe that GS is a game changer , would be extremely difficult if not fatal. If AF447 had maintained 450 kts and not changed pitch and power we wouldn’t be having the tenth anniversary this week of 300+ deaths.
So I am sorry, attempting to use a maths error in an otherwise proven scenario won’t change the science!
thanks for pointing out the error though. I wii shortly write an error free version which I will invite you to take apart on a factual basis!
y
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Old 2nd Jun 2019, 08:17
  #77 (permalink)  
 
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GS is a pretty foolproof way of avoiding calamity in serious confusing UAS situations with multiple distractions.
So is applying the memory items and/or NNCs laid down by the manufacturer.

If AF447 had maintained 450 kts and not changed pitch and power we wouldn’t be having the tenth anniversary this week of 300+ deaths.
If AF447 had simply not changed pitch or power, with no reference to GS at all, the same would still be true.

It’s quite true that GS has its uses - the ‘Reference GS’ we used to use on approach in Boeings, and the similar GS Mini in the Airbus are good examples. But I don’t agree that GS is the infallible all-purpose solution you seem to believe it is, nor can you justify using it instead of the manufacturer’s procedures.

While the two major errors you’ve made so far in your justifications can be dismissed as mere typos or because it was late or something, the fact is you still made them, at zero kts, 1 G, and without the pressure of “sudden chaotic UAS + SHAKER + MULTIPLE WARNING”. It’s not really a great advertisement for what you’re trying to sell.
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Old 2nd Jun 2019, 08:18
  #78 (permalink)  
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Originally Posted by hans brinker View Post
Yeah, I'm sure they would have had an accurate ground wind reading for AF 447.


Never mind that I've seen wind speed over 150kts without hurricane warnings on the ground.


https://www.pprune.org/professional-...nd-studies-14/
AF 447 and similar UAS incidents
The wind speed at the time of the pitot tube failure was right in front of the pilots as was the GS. Didn’t need ATC.
And the wind is available on every operational flight plan for every leg +/- 5 kts.
Had they done nothing which is what is recommended other than maintain existing steady state conditions inc. PITCH. POWER. GS we wouldn’t be having this conversation.
y
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Old 2nd Jun 2019, 08:27
  #79 (permalink)  
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Originally Posted by itsnotthatbloodyhard View Post


So is applying the memory items and/or NNCs laid down by the manufacturer.



If AF447 had simply not changed pitch or power, with no reference to GS at all, the same would still be true.

It’s quite true that GS has its uses - the ‘Reference GS’ we used to use on approach in Boeings, and the similar GS Mini in the Airbus are good examples. But I don’t agree that GS is the infallible all-purpose solution you seem to believe it is, nor can you justify using it instead of the manufacturer’s procedures.
I didn’t say instead of. I said in addition to. First response is always to stabilize using known PITCH POWER ALTITUDE WEIGHT ETC.
The existing steady state conditions are of course proven to work since that’s what you had just before the problem.
I repeat if AF 447 for example had done this they could not have stalled or indeed over speeded.
But after that you have to use a lot of logic to determine which if any or indeed all parameters are incorrect. And here GS is king. And as we can see here, there are people who don’t believe it! Good luck with that.
Y
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Old 2nd Jun 2019, 08:40
  #80 (permalink)  
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Sorry. Someone just asked “ but if AF had just set PITCH POWER etc that should have been enough”
It would have been a good start. But pitch/power can be out by significant margins which can over the next few seconds / minutes degrade the condition. Speed can start falling if power say 2% too low say., due to ISA + 20 for example.
Nose needs to go up. Speed falls more YOU DONT KNOW THIS unless you notice your ground speed falling below where it was, or lower than flight plan.
essentially this is the very point. To sit there allowing the speed to change and knowing it’s happening is - well , not a good idea and can easily lead to
loss of control. I’ve seen this technique used successfully in the sim. Over and over and it works with no drama at all.
Cheers
y
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