Max demonstrated crosswind definition please
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Max demonstrated crosswind definition please
Hi all!
I can't seem to get a definitive answer to this. What does "Max demonstrated X-wind" actually mean?
Is it:
A) Most crosswind the aircraft has been landed in without kicking off drift (crab technique).
B) Most crosswind the aircraft has been landed in with drift kicked off (crab technique).
C) Most demonstrated using wing down method.
D) None of the above.
As a footnote, what percentage of Vref would you say is the max theoretical crosswind if you use crab technique and kick the drift off. I've done 25kts X-wind in a 152 (Vref: 65) so 25/65 * 100 = 38%
TIA
I can't seem to get a definitive answer to this. What does "Max demonstrated X-wind" actually mean?
Is it:
A) Most crosswind the aircraft has been landed in without kicking off drift (crab technique).
B) Most crosswind the aircraft has been landed in with drift kicked off (crab technique).
C) Most demonstrated using wing down method.
D) None of the above.
As a footnote, what percentage of Vref would you say is the max theoretical crosswind if you use crab technique and kick the drift off. I've done 25kts X-wind in a 152 (Vref: 65) so 25/65 * 100 = 38%
TIA
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Not a factory test pilot myself, but on every type I was rated, max demonstrated xwind is less than max structural xwind (there often are engineering limits on gear) and generally the highest xwind the factory test pilot was landing the airplane at during the certification flights employing any technique to keep the airplane on the runway. Note that for some types you can't bank much at all during flare or you'll scrape ground with the engine pods.
Cheers
Doc
Cheers
Doc
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In the Part 25 world (or my part of it) it means the maximum demonstrated using the recommended technique - the technique we recommend is the one we (have to) use for the certification demonstration - as indeed is the case for all the procedures. We're not allowed (supposed) to use one procedure to demonstrate a compliance item, then recommend line pilots do something else. (This would apply to, for example, field performance data - if we stood on the brakes to get max braking, we have to include that in the procedures as well, at least so you know how to get our numbers when you need them)
you can't bank much at all during flare or you'll scrape ground with the engine pods
GF
Worth learning to land by squeezing out the crab on touchdown. Don't "kick" it out--had an Lt do that, took several years away.
Pedantic Watch--one doesn't "kick" out the drift-one kicks out the crab angle used to cancel out the drift.
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Don't "kick" it out--
If this was tried on the older longbody B707's, the 'kick' would more than likely result is dragging the engine pods on the downwind side.
AC 23-8B
107. SECTION 23.233 DIRECTIONAL STABILITY AND CONTROL.
a. Explanation.
(1) Crosswind. This regulation establishes the minimum value of crosswind that must be demonstrated. Since the minimum required value may be far less than the actual capability of the airplane, higher values may be tested at the option of the applicant. The highest 90- degree crosswind component tested satisfactorily should be put in the AFM as performance information. If a demonstrated crosswind is found limiting, it has to be introduced in Section 2 of the AFM.
b. Procedures.
(1) Crosswind.
(a) The airplane should be operated throughout its approved loading envelope at gradually increasing values of crosswind component until a crosswind equivalent to 0.2 VSO is reached. All approved takeoff and landing configurations should be evaluated. Higher crosswind values may be evaluated at the discretion of the test pilot for AFM inclusion.
(Part 25 requires a minimum of at least 20 kt.)
107. SECTION 23.233 DIRECTIONAL STABILITY AND CONTROL.
a. Explanation.
(1) Crosswind. This regulation establishes the minimum value of crosswind that must be demonstrated. Since the minimum required value may be far less than the actual capability of the airplane, higher values may be tested at the option of the applicant. The highest 90- degree crosswind component tested satisfactorily should be put in the AFM as performance information. If a demonstrated crosswind is found limiting, it has to be introduced in Section 2 of the AFM.
b. Procedures.
(1) Crosswind.
(a) The airplane should be operated throughout its approved loading envelope at gradually increasing values of crosswind component until a crosswind equivalent to 0.2 VSO is reached. All approved takeoff and landing configurations should be evaluated. Higher crosswind values may be evaluated at the discretion of the test pilot for AFM inclusion.
(Part 25 requires a minimum of at least 20 kt.)
Moderator
Since the minimum required value may be far less than the actual capability of the airplane
Conversely, it may be very close to the demonstrated value eg the Rockwell Commander singles, when they were introduced to Australia, came with a 15 kt X/W, as I recall.
One intrepid DCA TP (CJF) and I redid the test points and frightened ourselves at around 18 kts which was reasonably limiting. Not having looked at any recent Commander flight manuals, I don't know if the 18 kt limit still exists or if, with the transition to OEM manuals, it has gone back to 15 kt. Nice birds but never did like interconnected controls.
If everyone were to be trained on Supercubs, crosswinds wouldn't be a problem .. just a personal view, mind you.
Conversely, it may be very close to the demonstrated value eg the Rockwell Commander singles, when they were introduced to Australia, came with a 15 kt X/W, as I recall.
One intrepid DCA TP (CJF) and I redid the test points and frightened ourselves at around 18 kts which was reasonably limiting. Not having looked at any recent Commander flight manuals, I don't know if the 18 kt limit still exists or if, with the transition to OEM manuals, it has gone back to 15 kt. Nice birds but never did like interconnected controls.
If everyone were to be trained on Supercubs, crosswinds wouldn't be a problem .. just a personal view, mind you.
For small aircraft (FAA part 23/CAR3) the certification requirement is the aircraft must be able to handle a cross wind value of 20 % of VSo. For most light aircraft this would be a very low value so the test pilots demonstrate the aircraft can land at a higher wind speed. But the value is not limiting and in the case of SE Cessna's is IMO quite conservative.
For small aircraft (FAA part 23/CAR3) the certification requirement is the aircraft must be able to handle a cross wind value of 20 % of VSo. For most light aircraft this would be a very low value so the test pilots demonstrate the aircraft can land at a higher wind speed.
An important part of the definition of ‘max demonstrated’ is that “The airplane must be satisfactorily controllable without requiring exceptional piloting skill or strength.”
However, without any definition of exceptional piloting skill, the judgment of an individual’s skill is open to bias and enables an erroneous attempt to land when it should not be contemplated.
Often wind gusts and errors in wind measurement are not considered, nor is the ability to keep the aircraft on the runway after achieving the landing – there are many differing standards of runway surfaces (plus wet / slippery) which require respectful reduction in crosswind limits.
Pilots should consider carefully when they last demonstrated their ‘near exceptional’ skill. Consider if max wind conditions have been experienced before, if not then an attempt to land is similar to the manufacturer’s test flights, but it involves demonstrating (a real time assessment) individual ‘skill’ in the prevailing conditions, which may not be the same as would be chosen for test flights, they choose when to do the landing tests.
I agree with JT, and that the text in FAR 23 is misleading – you don’t know where the aircraft’s limit is or what the combined effect with your personal limit will be. All interpretations and assessments should be a rounding down of what is published. Just a personal opinion, but from someone who has demonstrated a few limits – aircraft and personal.
However, without any definition of exceptional piloting skill, the judgment of an individual’s skill is open to bias and enables an erroneous attempt to land when it should not be contemplated.
Often wind gusts and errors in wind measurement are not considered, nor is the ability to keep the aircraft on the runway after achieving the landing – there are many differing standards of runway surfaces (plus wet / slippery) which require respectful reduction in crosswind limits.
Pilots should consider carefully when they last demonstrated their ‘near exceptional’ skill. Consider if max wind conditions have been experienced before, if not then an attempt to land is similar to the manufacturer’s test flights, but it involves demonstrating (a real time assessment) individual ‘skill’ in the prevailing conditions, which may not be the same as would be chosen for test flights, they choose when to do the landing tests.
I agree with JT, and that the text in FAR 23 is misleading – you don’t know where the aircraft’s limit is or what the combined effect with your personal limit will be. All interpretations and assessments should be a rounding down of what is published. Just a personal opinion, but from someone who has demonstrated a few limits – aircraft and personal.
Moderator
the text in FAR 23 is misleading
If one is interested in what might have gone into a particular Type's certification, it is necessary to read, at the very least -
(a) TCDS to determine the rules applicable to the certification
(b) CAR/FAR relevant to (a)
(c) the relevant AC 23-8 which gives you the basics on what the FT certification community were looking at for the certification. There probably was a predating document for earlier Types but I can't bring that to mind at the moment.
If one is interested in what might have gone into a particular Type's certification, it is necessary to read, at the very least -
(a) TCDS to determine the rules applicable to the certification
(b) CAR/FAR relevant to (a)
(c) the relevant AC 23-8 which gives you the basics on what the FT certification community were looking at for the certification. There probably was a predating document for earlier Types but I can't bring that to mind at the moment.
John… and perhaps AC 25 -7A “Flight Test Guide”, which although it is for transport category aircraft is AFAIK the only guide to flight tests that is used across a range of aircraft categories.
A particular hazard of the Part 23 wording is that pilots whom move up to Part 25 aircraft from aircraft with lower standards might take their ‘lower’ understanding with them. I don’t recall any ‘differences’ training covering the certification standards when converting to larger aircraft.
A particular hazard of the Part 23 wording is that pilots whom move up to Part 25 aircraft from aircraft with lower standards might take their ‘lower’ understanding with them. I don’t recall any ‘differences’ training covering the certification standards when converting to larger aircraft.
Moderator
For most light aircraft this would be a very low value
Given, for most lighties, that the design limit for stall is 70 mph (61 kts if you prefer the new-fangled stuff), generally we will be looking for something in the 10-15kt region. (The 70 mph thing dates back to the real olden days and was a finger in the wind figure thought to be a reasonable speed to provide some sensible likelihood of surviving a crash landing off airport .. which was the norm in those days of yesteryear).
10-15 kts is fine if you stick to places with lots of runways.
The important points to keep in mind -
(a) the OEM generally will endeavour to get the highest X/W they can for marketing but are limited by what they can get. No-one is going to waste too much time chasing wind for a diminishing return, so long as the certification requirements can be ticked off.
(b) the demonstrated value may be limiting, or near-limiting, which was the reason I introduced the Commander anecdote
(c) the demonstrated value may be significantly non-limiting, which gives rise to the hangar tales of "there I was landing in (pick a figure) knots X/W". We've all done that but there is a need to remember that the onus is on the pilot to be able to justify his actions at the enquiry (read insurance consequence, in particular) if the operation goes pear shaped.
Many of us have frightened ourselves with higher than prudent X/W - I recall being caught out as a young buck with a gusting X/W which my inexperience allowed to put the downwind wingtip VERY close to the runway. Fortunately, I was able to drag the bird back off the ground and do a bit better on the next landing so I didn't have to explain my actions. However, I did learn a sobering lesson along the way.
The advantage of sticking with demonstrated as a defacto limit is that the certification system has had a reasonable look at that sort of wind level. One needs to keep in mind that the certification exercise will have been done in reasonably smooth wind conditions. If the day is strongly gusting, one needs to have a very circumspect think about whether it might be a good idea to land someplace else.
I don’t recall any ‘differences’ training covering the certification standards when converting to larger aircraft.
I'm a tad out of touch with the training side these days but I suspect that the general knowledge level of certification amongst the usual pilot ranks is pretty shallow .. one of the values of Tech Log given that we have a few certification folk who play regularly in this sand pit.
When I were but a young lad the training paradigm in Oz was a reasonably good background in performance certification but next to nothing elsewhere .. better than nothing, I guess ?
Flight Test Guides
I commend these documents for a read. Not light going but gives a better appreciation of the sorts of things which go into the performance and handling side of certification than you ever got in flight training courses.
(a) lighties at AC 23-8B
(b) heavy metal at AC 25-7A
Given, for most lighties, that the design limit for stall is 70 mph (61 kts if you prefer the new-fangled stuff), generally we will be looking for something in the 10-15kt region. (The 70 mph thing dates back to the real olden days and was a finger in the wind figure thought to be a reasonable speed to provide some sensible likelihood of surviving a crash landing off airport .. which was the norm in those days of yesteryear).
10-15 kts is fine if you stick to places with lots of runways.
The important points to keep in mind -
(a) the OEM generally will endeavour to get the highest X/W they can for marketing but are limited by what they can get. No-one is going to waste too much time chasing wind for a diminishing return, so long as the certification requirements can be ticked off.
(b) the demonstrated value may be limiting, or near-limiting, which was the reason I introduced the Commander anecdote
(c) the demonstrated value may be significantly non-limiting, which gives rise to the hangar tales of "there I was landing in (pick a figure) knots X/W". We've all done that but there is a need to remember that the onus is on the pilot to be able to justify his actions at the enquiry (read insurance consequence, in particular) if the operation goes pear shaped.
Many of us have frightened ourselves with higher than prudent X/W - I recall being caught out as a young buck with a gusting X/W which my inexperience allowed to put the downwind wingtip VERY close to the runway. Fortunately, I was able to drag the bird back off the ground and do a bit better on the next landing so I didn't have to explain my actions. However, I did learn a sobering lesson along the way.
The advantage of sticking with demonstrated as a defacto limit is that the certification system has had a reasonable look at that sort of wind level. One needs to keep in mind that the certification exercise will have been done in reasonably smooth wind conditions. If the day is strongly gusting, one needs to have a very circumspect think about whether it might be a good idea to land someplace else.
I don’t recall any ‘differences’ training covering the certification standards when converting to larger aircraft.
I'm a tad out of touch with the training side these days but I suspect that the general knowledge level of certification amongst the usual pilot ranks is pretty shallow .. one of the values of Tech Log given that we have a few certification folk who play regularly in this sand pit.
When I were but a young lad the training paradigm in Oz was a reasonably good background in performance certification but next to nothing elsewhere .. better than nothing, I guess ?
Flight Test Guides
I commend these documents for a read. Not light going but gives a better appreciation of the sorts of things which go into the performance and handling side of certification than you ever got in flight training courses.
(a) lighties at AC 23-8B
(b) heavy metal at AC 25-7A
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A flight examiners interpretation during a flight test was the maximum crosswind velocity where the aircraft will still conform to the flight manual data in terms of take-off and landing distance (short-field technique).
More crosswind is possible, except to get the necessary rudder authority in the flare to straighten the nose requires a higher approach speed which will increase landing distance.
More crosswind is possible, except to get the necessary rudder authority in the flare to straighten the nose requires a higher approach speed which will increase landing distance.
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In some cases there may be an AFM perf correction at higher crosswinds anyway, so looking at the perf data for the crosswind limit really isn't the right place to look.
Crosswind demonstrations or limits is handling; perf is perf. They are related, but it's not the prime relationship.
Crosswind demonstrations or limits is handling; perf is perf. They are related, but it's not the prime relationship.
Creep warning - Not crosswind but still demonstrated handling:
Recollect asking boss why higher powered version of our twinjet had a lower stated Vmcg than our lower powered version.
His explanation was that was what the test pilot demonstrated on the day.
I dunno whether the fin/rudder was different.
Recollect asking boss why higher powered version of our twinjet had a lower stated Vmcg than our lower powered version.
His explanation was that was what the test pilot demonstrated on the day.
I dunno whether the fin/rudder was different.
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My understanding of "maximum demonstrated crosswind" is the maximum crosswind that was use for the certification of the aircraft.
Obviously you would be waiting a long time for the conditions to be AT the maximum crosswind limits during the certification period.
The B777 max demontrated crosswind is 38kts for take-off and landing, however the maximum certified limit is 40kts depending on R/W conditions.
Oz
Obviously you would be waiting a long time for the conditions to be AT the maximum crosswind limits during the certification period.
The B777 max demontrated crosswind is 38kts for take-off and landing, however the maximum certified limit is 40kts depending on R/W conditions.
Oz
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It is also the value which if exceeded, and an accident ensues, provides your insurer with a convenient means of escape as you have exceeded the limits contained in the POH!!
This discussion jogged a faint memory so I went looking and found this which is an extract from here,
"2004 Flight Operations Symposium Questions May 9 – 12, 2004, Bell Harbor Convention Center"
20. Are the published crosswind guidelines piloted simulations?
<Answer>. The 737 classic, the 757, the 767 and the 777 takeoff crosswind guidelines are based on piloted cab simulations assuming an engine out refused takeoff maneuver at an adverse loading condition using normal piloting techniques. The published crosswinds were selected to provide adequate airplane control. The 737NG and 747 takeoff crosswind guidelines are based on engineering analysis and simulation studies assuming the same
engine out refused takeoff maneuver.
The 737 classic, 737NG, 747-400, 757, 767, and 777 landing crosswind guidelines are based on piloted cab simulations at an adverse loading condition using normal piloting techniques. Both all engines operating and engine out landings were considered. As above, the published crosswinds were selected to provide adequate airplane control.
21. What is the difference between the crosswind guidelines and the demonstrated crosswind data in the airplane flight manual?
<Answer>. The AFM "demonstrated" value is simply the highest crosswind conditions that were encountered during the airplane flight test program. The recommended crosswind limits were determined by analysis and piloted simulator evaluation, not by flight test.
An interesting comment, the last sentence.
Regards,
BH
"2004 Flight Operations Symposium Questions May 9 – 12, 2004, Bell Harbor Convention Center"
20. Are the published crosswind guidelines piloted simulations?
<Answer>. The 737 classic, the 757, the 767 and the 777 takeoff crosswind guidelines are based on piloted cab simulations assuming an engine out refused takeoff maneuver at an adverse loading condition using normal piloting techniques. The published crosswinds were selected to provide adequate airplane control. The 737NG and 747 takeoff crosswind guidelines are based on engineering analysis and simulation studies assuming the same
engine out refused takeoff maneuver.
The 737 classic, 737NG, 747-400, 757, 767, and 777 landing crosswind guidelines are based on piloted cab simulations at an adverse loading condition using normal piloting techniques. Both all engines operating and engine out landings were considered. As above, the published crosswinds were selected to provide adequate airplane control.
21. What is the difference between the crosswind guidelines and the demonstrated crosswind data in the airplane flight manual?
<Answer>. The AFM "demonstrated" value is simply the highest crosswind conditions that were encountered during the airplane flight test program. The recommended crosswind limits were determined by analysis and piloted simulator evaluation, not by flight test.
An interesting comment, the last sentence.
Regards,
BH