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PostPosted: Sat Oct 22, 2016 8:21 pm 
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When landing with a strong headwind, is it necessary to increase power.

For example, if normal approach speed is 80 knots and you are landing with a 25 knot headwind, should power be increased to achieve 105 knots IAS? Maybe somewhere in between 80-105?

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PostPosted: Sat Oct 22, 2016 9:09 pm 
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No because the airplane, specifically the wings do not care what their speed over the ground is. You take whatever ground speed you get. Now you might elect to fly an approach faster and then configure for final approach a little later to cover more ground, but in the end, the IAS on the airspeed indicator will still dictate the performance of the wings as you land.

Depending on the airplane you are flying, the approach might end up looking very steep, uncomfortably steep, even though it is flown at normal speeds.

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PostPosted: Sun Oct 23, 2016 1:33 am 
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Just to add to Oracles post. This is exactly the reason you takeoff and land into the wind. Sticking with your example. In a 25 knot headwind with a 80 knot ias approach you have a ground speed of 55 knots. This is the speed you'll have to get rid of once you touched down. So you have a shorter landing distance then usually.

If you would land with a 25 knots tailwind in this example you would touch down with 105 knots. This may result in some serious trouble of keeping the airplane on the runway after touchdown because your landing distance will be very long.

You might want to add a couple of knots to your approach speed if the wind is very gusty but you do not need to compensate for headwind in respect to the IAS.

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PostPosted: Sun Oct 23, 2016 8:56 am 
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Thanks guys.

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PostPosted: Sun Oct 23, 2016 10:37 am 
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This is different from your usual airline SOPs where you would add half the headwind component plus the full gust increment to whatever Vref you calculate. No idea why, but a guess would be that for the case that the wind will suddenly change, let's say to a full crosswind, jet engines usually take a lot longer to spool up in order to correct for that loss of airspeed than a piston engine takes.


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PostPosted: Mon Oct 24, 2016 4:51 am 
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What we do we keep the same IAS but add 100/200 rpm power so as to decrease the verticalspeed. On final you may consider not employing flaps to the full.

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PostPosted: Mon Oct 24, 2016 7:48 am 
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Oliver Branaschky wrote:
This is different from your usual airline SOPs where you would add half the headwind component plus the full gust increment to whatever Vref you calculate. No idea why, but a guess would be that for the case that the wind will suddenly change, let's say to a full crosswind, jet engines usually take a lot longer to spool up in order to correct for that loss of airspeed than a piston engine takes.


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This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.

Also, modern jet engines take very little time to respond to throttle changes, so that's not a consideration.

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PostPosted: Mon Oct 24, 2016 7:57 am 
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CAPFlyer wrote:
Oliver Branaschky wrote:
This is different from your usual airline SOPs where you would add half the headwind component plus the full gust increment to whatever Vref you calculate. No idea why, but a guess would be that for the case that the wind will suddenly change, let's say to a full crosswind, jet engines usually take a lot longer to spool up in order to correct for that loss of airspeed than a piston engine takes.


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This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.

Also, modern jet engines take very little time to respond to throttle changes, so that's not a consideration.


Great, thanks.


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PostPosted: Mon Oct 24, 2016 1:16 pm 
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CAPFlyer wrote:
This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.

Chris, I have never heard of such a thing. If one is always tacking on 5kts on the approach speed, it is doing something that is unnecessary. That isn't what I would call good airmanship.

• You have to remember, the airspeed given in the POH is normally for the airplane at max gross weight. So if you are not compensating for reduced weight, you already have that "fudge factor" built in.

• From the Private Pilot ACS: Maintain a stabilized approach and recommended airspeed, or in its absence, not more than 1.3 VSO, with wind gust factor applied +10/-5 knots . So, if one is within Private Pilot standards, that could put one 10 knots fast on final.

• Extra airspeed, along with poor flare technique, can lead to ballooning during the roundout - that could result in a hard landing.

• When carrying extra airspeed into the flare, the airplane will float until that speed bleeds off.

• If you touchdown with that extra airspeed your roll-out distance ratio will increase by the square of the ratio of your actual touchdown speed over your normal touchdown speed. So if your touchdown speed should be 40kts, and you touchdown at 45kts - 45/40 is 1.13 so that is 13% faster than you need to be. Square that - and you will require 27% more runway to roll out.

When you do add a gust factor, the typical rule of thumb is 1/2 the gust. So if the winds are 10kts gusting to 20kts, then you would add 5kts.

-Rob

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PostPosted: Mon Oct 24, 2016 1:42 pm 
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Great Ozzie wrote:
CAPFlyer wrote:
This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.

Chris, I have never heard of such a thing. If one is always tacking on 5kts on the approach speed, it is doing something that is unnecessary. That isn't what I would call good airmanship.

• You have to remember, the airspeed given in the POH is normally for the airplane at max gross weight. So if you are not compensating for reduced weight, you already have that "fudge factor" built in.

• From the Private Pilot ACS: Maintain a stabilized approach and recommended airspeed, or in its absence, not more than 1.3 VSO, with wind gust factor applied +10/-5 knots . So, if one is within Private Pilot standards, that could put one 10 knots fast on final.

• Extra airspeed, along with poor flare technique, can lead to ballooning during the roundout - that could result in a hard landing.

• When carrying extra airspeed into the flare, the airplane will float until that speed bleeds off.

• If you touchdown with that extra airspeed your roll-out distance ratio will increase by the square of the ratio of your actual touchdown speed over your normal touchdown speed. So if your touchdown speed should be 40kts, and you touchdown at 45kts - 45/40 is 1.13 so that is 13% faster than you need to be. Square that - and you will require 27% more runway to roll out.

When you do add a gust factor, the typical rule of thumb is 1/2 the gust. So if the winds are 10kts gusting to 20kts, then you would add 5kts.

-Rob


Rob, we were talking about airline operations here. From the Boeing 737-7/8/900 Flight Crew Operations Manual, 1.16 and 1.17: "If the autothrottle is disengaged, or is planned to be disengaged prior to landing, the recommended method for approach speed correction is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed (...) The minimum command speed setting with autothrottle disconnected is VREF + 5 knots. The gust correction should be maintained to touchdown while the steady headwind correction should be bled off as the airplane approaches touchdown."

Best regards,
Oliver


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PostPosted: Mon Oct 24, 2016 3:49 pm 
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Oliver Branaschky wrote:
Rob, we were talking about airline operations here.

Hi Oliver,

Thanks for making that clear.

-Rob

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PostPosted: Mon Oct 24, 2016 5:37 pm 
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Oliver Branaschky wrote:
Great Ozzie wrote:
CAPFlyer wrote:
This is simply a "fudge factor" in case there is undetected low-level windshear. Gusty winds increase the chance of windshear, thus the full component add and you can have windshear with nearly any wind. Also, unless the headwind is over 10 knots, most pilots don't add anything because most of the time you fly VREF+5 anyway.

Chris, I have never heard of such a thing. If one is always tacking on 5kts on the approach speed, it is doing something that is unnecessary. That isn't what I would call good airmanship.

• You have to remember, the airspeed given in the POH is normally for the airplane at max gross weight. So if you are not compensating for reduced weight, you already have that "fudge factor" built in.

• From the Private Pilot ACS: Maintain a stabilized approach and recommended airspeed, or in its absence, not more than 1.3 VSO, with wind gust factor applied +10/-5 knots . So, if one is within Private Pilot standards, that could put one 10 knots fast on final.

• Extra airspeed, along with poor flare technique, can lead to ballooning during the roundout - that could result in a hard landing.

• When carrying extra airspeed into the flare, the airplane will float until that speed bleeds off.

• If you touchdown with that extra airspeed your roll-out distance ratio will increase by the square of the ratio of your actual touchdown speed over your normal touchdown speed. So if your touchdown speed should be 40kts, and you touchdown at 45kts - 45/40 is 1.13 so that is 13% faster than you need to be. Square that - and you will require 27% more runway to roll out.

When you do add a gust factor, the typical rule of thumb is 1/2 the gust. So if the winds are 10kts gusting to 20kts, then you would add 5kts.

-Rob


Rob, we were talking about airline operations here. From the Boeing 737-7/8/900 Flight Crew Operations Manual, 1.16 and 1.17: "If the autothrottle is disengaged, or is planned to be disengaged prior to landing, the recommended method for approach speed correction is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed (...) The minimum command speed setting with autothrottle disconnected is VREF + 5 knots. The gust correction should be maintained to touchdown while the steady headwind correction should be bled off as the airplane approaches touchdown."

Best regards,
Oliver


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It should be strongly noted that regulations are regulations and IAS, TAS, and GS are the result of aerodynamics and engineering. The aerodynamics can be the same while the regulations governing how the aircraft must handle the aerodynamics can and does differ greatly.

The regs might differ as to the circumstances pertaining to approaches between airline operations and GA operations but the factors actually affecting the plane on approach are virtually the same be it a 747 or a Cessna 150.
I know...........its a fine point, but as we say in the airshow business when we start talking about density altitude,
"Indicated airspeed is indicated airspeed................but true airspeed is another matter. " :-))
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PostPosted: Tue Jan 03, 2017 8:38 am 
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Chris is correct. Every airline I've flown for requires us to add a minimum of five knots to REF. That applies to everything from the Q-400 up to the 757/767 I fly now. 5 knots is added to every approach, even if winds are calm, up to a maximum of REF+20 if the winds are really howling.

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