Headwind additive for autothrottle use.
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Headwind additive for autothrottle use.
Wondering,what is the headwind component additive on the Vref for an approach with autothrottles on.Say an autoland,or,for that matter even a manual landing with autothrottles on.
Normal sop's dictate Vref+5 kts.But what if the wind is say 20 kts headwind gusting to 30 kts.Still the same.....???!?
Cheers...
Normal sop's dictate Vref+5 kts.But what if the wind is say 20 kts headwind gusting to 30 kts.Still the same.....???!?
Cheers...
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strg+c strg+v....don't u love it?
During autothrottle operation, when on final approach in landing configuration,
it is not recommended to set the A/T command speed to allow for wind or gust
corrections. Through airspeed and acceleration sensing, the A/T corrects for
normal wind gusts. Higher command speed settings result in excessive
approach speeds. The A/T approach speed setting is Vref +5.
it is not recommended to set the A/T command speed to allow for wind or gust
corrections. Through airspeed and acceleration sensing, the A/T corrects for
normal wind gusts. Higher command speed settings result in excessive
approach speeds. The A/T approach speed setting is Vref +5.
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Half the headwind, plus all of the gust. In your case 20/2=10 + 10 (Difference between 30-20 is the gust) there for 10+10= 20 so your fly speed would be Vref + 20. Some operators use a correction up to a maximum of 15 knots. Sometimes your fly speed might take you close to the flap limiting speed then in this case it's the flap limit minus 5 knots.
I can only speak for my type. So other guys might have different take on it, but the general principal is usually the same.
IR
I can only speak for my type. So other guys might have different take on it, but the general principal is usually the same.
IR
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@Robin & FCS.....what about airplanes that land with autothrottles on but autopilot off for manual landings.As in the 777 maybe.Does the Vref+5 rule still apply? And why is that?
As far as I know, the autothrottle on a large aircraft is FAR slower and more sluggish to react to a change in speed than a pilot controlling the speed on manual thrust.So why the lower additive on automatics than on manuals?The same holds true for an increase in speed....slow on auto than on manual.
Still wondering why...
Thx for all the replies so far.
As far as I know, the autothrottle on a large aircraft is FAR slower and more sluggish to react to a change in speed than a pilot controlling the speed on manual thrust.So why the lower additive on automatics than on manuals?The same holds true for an increase in speed....slow on auto than on manual.
Still wondering why...
Thx for all the replies so far.
FCS Explorer is not expressing a pet theory - he is quoting verbatim the Boeing 737 Flight Crew Training Manual. Vref + 5 is the number for that type - applicable to all series fitted with autothrottle from the -200 ADV to the latest.
Note the use of the word 'recommended'.
Only once have I seen a statement in a company operating manual that quite clearly said that they had developed some differing procedures as a result of extensive operational experience, that their procedures were FAA approved, and that they accepted responsibility for the consequences of having changed the procedures. In the absence of that statement, I have always assumed that if a company issues crews with the Boeing FCTM, the intent is for it to over ride the SOP in much the same way as the AFM does.
Note the use of the word 'recommended'.
Only once have I seen a statement in a company operating manual that quite clearly said that they had developed some differing procedures as a result of extensive operational experience, that their procedures were FAA approved, and that they accepted responsibility for the consequences of having changed the procedures. In the absence of that statement, I have always assumed that if a company issues crews with the Boeing FCTM, the intent is for it to over ride the SOP in much the same way as the AFM does.
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Mach.....not so for the 777's.Landing manually with autothrottle on is NORMAL procedure there.The 737 is a whole different ballgame...autopilot and autothrottle are extremely degraded with comparison to the 777's..
Autothrust is recommended for all approaches and landings in the B777.
From the B777 FCTM:
"When using the auto-throttle, position command speed to VREF + 5 kt. Sufficient wind and gust protection is available with the auto-throttle engaged because the auto-throttle is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing thrust slowly when the airspeed exceeds command speed. In turbulence, the result is that average thrust is higher than necessary to maintain command speed. This results in an average speed exceeding command speed."
From the B777 FCTM:
"When using the auto-throttle, position command speed to VREF + 5 kt. Sufficient wind and gust protection is available with the auto-throttle engaged because the auto-throttle is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing thrust slowly when the airspeed exceeds command speed. In turbulence, the result is that average thrust is higher than necessary to maintain command speed. This results in an average speed exceeding command speed."
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As far as I know, the autothrottle on a large aircraft is FAR slower and more sluggish to react to a change in speed than a pilot controlling the speed on manual thrust.
It appears that you might be just a tad misinformed.
On the Lockheed tri-motor, just as one example, the autothrottles are very fast acting so...Vref+5 is quite satisfactory.
And, as this is a rather older design, I'm quite sure newer (especially Boeing) types would be just as good, or better.
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411.....thx
Unfortunately,I've heard u mention the "lockheed tri motor" about 5000 times in ur six odd thousand posts.Wonder why.Maybe cause that's ur last airplane flown? I appreciate ur emotions,but not ur knowledge.
That said,I of course am well aware of what the B777 fctm says Buzzbox.I was very categorically asking for personal opinions here.And not quotes from boring self centered hardcopies that boeing publishes to cover its back side! Well,if they said fly Vref in microburst conditions,just to sell their new airplanes,would u do that.I certainly wouldn't.
They also said the GE 115 would have less than 6 engine failures per million cycles so that they could sell the same (and yes there is a covert handshake between Boeing and GE).But we now know that not to be true.
So whats your personal take on this command speed.And believe me,i'm looking for an experienced personal viewpoint.The books are for all the 6.2 billion of us to see.
The reasoning behind those books however,are for but 6 odd good ones to understand and challenge.Am looking for those 6 thankfully.....
Thanks.
@411-you are an extremely experienced aviator.I acknowledge and salute that.Pls don't take my remarks incorrectly.I am just looking for genuine opinion...
Cause i'm just NOT convinced...
And when i said 'as far as i know'....it meant just that.Not meant to be mis quoted,rather understood.And i DO know quite a bit...
Unfortunately,I've heard u mention the "lockheed tri motor" about 5000 times in ur six odd thousand posts.Wonder why.Maybe cause that's ur last airplane flown? I appreciate ur emotions,but not ur knowledge.
That said,I of course am well aware of what the B777 fctm says Buzzbox.I was very categorically asking for personal opinions here.And not quotes from boring self centered hardcopies that boeing publishes to cover its back side! Well,if they said fly Vref in microburst conditions,just to sell their new airplanes,would u do that.I certainly wouldn't.
They also said the GE 115 would have less than 6 engine failures per million cycles so that they could sell the same (and yes there is a covert handshake between Boeing and GE).But we now know that not to be true.
So whats your personal take on this command speed.And believe me,i'm looking for an experienced personal viewpoint.The books are for all the 6.2 billion of us to see.
The reasoning behind those books however,are for but 6 odd good ones to understand and challenge.Am looking for those 6 thankfully.....
Thanks.
@411-you are an extremely experienced aviator.I acknowledge and salute that.Pls don't take my remarks incorrectly.I am just looking for genuine opinion...
Cause i'm just NOT convinced...
And when i said 'as far as i know'....it meant just that.Not meant to be mis quoted,rather understood.And i DO know quite a bit...
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KoaW - in my 20 years or so on the 737 I have never found Vref+5 to work in anything other than a steady 10 kts down the runway. The 737 A/T is notoriously poor at maintaining a 'suitable' speed, and there is also the problem, when/if you disengage it on the approach with Vref+5 set, of having to then increase the 'dialled' speed to cope with headwind/gusts. In my experience most folk dial the 'corrected speed' into the window and the A/T has more or less coped with that. Only problem there is if you ever land with the A/T engaged (non-autoland) you could be outside the 'margin' allowed for landing perf. On CAT II/IIIs the wind limits are such that the problem does not normally arise.
I have generally bugged 'what I want' with A/T engaged and if it is flying me too fast, taken it out. The key with all things 'automatic' on a/c is to see if they are doing what you want, and if not, take them out (or is that modern-day heresy.....)
I have generally bugged 'what I want' with A/T engaged and if it is flying me too fast, taken it out. The key with all things 'automatic' on a/c is to see if they are doing what you want, and if not, take them out (or is that modern-day heresy.....)
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I agree with your thought BOAC.
Unfortunately the 737 was NOT designed to be flown manually with the A/T engaged..(FMS not in sync with the A/T etc etc).Thus the obvious issues of 'dialling up' the approach speed on disconnecting A/T for landing.However,larger jets ARE designed to be flown manually WITH the A/T engaged and ON.All the way to reverse thrust.Wherein the A/T automatically disconnects.But is still armed.
Therefore doesn't the 737 logic apply on these larger jets?
That is.....fly the higher speed upto touchdown?
Or are we presuming an extremely responsive A/T all the way to touchdown...?? Which obviously comes with its cons of HUGE pitch changes very close to the ground in gusting conditions.Which gets me to the start of another thread......."Would you rather fly a gusty approach on autothrust or manual thrust"....
Well.....thats for another decade.....
Unfortunately the 737 was NOT designed to be flown manually with the A/T engaged..(FMS not in sync with the A/T etc etc).Thus the obvious issues of 'dialling up' the approach speed on disconnecting A/T for landing.However,larger jets ARE designed to be flown manually WITH the A/T engaged and ON.All the way to reverse thrust.Wherein the A/T automatically disconnects.But is still armed.
Therefore doesn't the 737 logic apply on these larger jets?
That is.....fly the higher speed upto touchdown?
Or are we presuming an extremely responsive A/T all the way to touchdown...?? Which obviously comes with its cons of HUGE pitch changes very close to the ground in gusting conditions.Which gets me to the start of another thread......."Would you rather fly a gusty approach on autothrust or manual thrust"....
Well.....thats for another decade.....
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On CAT II/IIIs the wind limits are such that the problem does not normally arise.
I was very categorically asking for personal opinions here.And not quotes from boring self centered hardcopies that boeing publishes to cover its back side!
Or are we presuming an extremely responsive A/T all the way to touchdown...?? Which obviously comes with its cons of HUGE pitch changes very close to the ground in gusting conditions.
"Would you rather fly a gusty approach on autothrust or manual thrust"
Well,if they said fly Vref in microburst conditions,just to sell their new airplanes,would u do that.I certainly wouldn't.
Last edited by BuzzBox; 5th Oct 2009 at 08:13.
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A real pilot has his/her hands on the thrust levers to beigin with and IF NECESSARY will move them accordingly to the conditions that exist. Otherwise do what Mr. Boeing says in the FCTM and add 5 knots assuming you intend to leave the A/Ts on through touchdown.
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Half the headwind, plus all of the gust
This suggests that if you have (say) a 15 knot half the HW component additive there is no way you can bleed this lot off in the flare. In fact, normal bleed off in the flare is three knots. Taking the argument a step further, I would hazard a guess (from frequent observation) and say the majority of HW component additives using manual throttle, are rarely bled off and are taken right down to the flare - resulting in many instances, a long float touch down.
The reason for the Boeing half the headwind additive is to cater for ground friction slowing the wind down below the free stream flow which starts around 1500-2000 ft agl. This means you should start bleeding away the half headwind component at that height so that in theory you arrive over the fence at Vref. If you do that without telling the PNF first, his screams of "SPEEED" from an uneducated PNF would likely waken the dead.. In which case tell him to read his Boeing FCTM or kindly pull his head in. Good CRM that, as he will undoubtly learn from your superior knowledge..
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If I may just inject someting....
There has been several quotes of the 737 FCTM so I won't add any more (mainly because I don't have it available)
Now, If we are manually man-handling the thrust levers we bug the whole headwind and half the gust and then aim for the bug. Later we bleed of some of that but that has already been discussed.
The autothrottle does things a little bit different (no surprise there, it is a 737 after all) it wants the bug to be set at +5knots but tht doesn't mean that it's aiming for it. Boeing engineerd this thing in the pre-byte (bite?) era and solved the problems by setting different speeds on the forward and retarding motions. The effect of this is that the autothrottle is incapable of maintaining the bug speed in anything else then conditions where the wind is completely stable and critically doesn't change with altitude. So what may appear as a rubbish autothrottle is a design feature so that the actual speed is always higher than the bug speed. the more gust or wind change that is encountered the higher the margin to the bug.
The real dilemma occurs if you intend to disengage the autothrottle at say 500'. If you bug +5 the autotrottle will fly at a speed in excess of it and one might argue that you would have to change the bug setting when you disengage.
If you choose the other option the autotrottle will now fly much to fast (in theory twice as much wind addative as you wanted and bugged) and it will be a handful to get rid of that speed eventually and you could potentially exceed the flap limit.
All above not withstanding the fact that the autothrottle is a not-to-be-trusted-piece-of &^%%^ in most scenarios!
signing off
There has been several quotes of the 737 FCTM so I won't add any more (mainly because I don't have it available)
Now, If we are manually man-handling the thrust levers we bug the whole headwind and half the gust and then aim for the bug. Later we bleed of some of that but that has already been discussed.
The autothrottle does things a little bit different (no surprise there, it is a 737 after all) it wants the bug to be set at +5knots but tht doesn't mean that it's aiming for it. Boeing engineerd this thing in the pre-byte (bite?) era and solved the problems by setting different speeds on the forward and retarding motions. The effect of this is that the autothrottle is incapable of maintaining the bug speed in anything else then conditions where the wind is completely stable and critically doesn't change with altitude. So what may appear as a rubbish autothrottle is a design feature so that the actual speed is always higher than the bug speed. the more gust or wind change that is encountered the higher the margin to the bug.
The real dilemma occurs if you intend to disengage the autothrottle at say 500'. If you bug +5 the autotrottle will fly at a speed in excess of it and one might argue that you would have to change the bug setting when you disengage.
If you choose the other option the autotrottle will now fly much to fast (in theory twice as much wind addative as you wanted and bugged) and it will be a handful to get rid of that speed eventually and you could potentially exceed the flap limit.
All above not withstanding the fact that the autothrottle is a not-to-be-trusted-piece-of &^%%^ in most scenarios!
signing off