Maximum permissible crosswind
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Maximum permissible crosswind
Hi
How are The maximum permissible crosswind for aircraft landing under different runway conditions (friction) is derived, i came across an article published by airbus, which gives max cross wind allowed for different runway friction levels for landings, was intersted to know how they came up with these values,
Is it simulation and/or there is some analytical procedure to calculate them?
thanks
How are The maximum permissible crosswind for aircraft landing under different runway conditions (friction) is derived, i came across an article published by airbus, which gives max cross wind allowed for different runway friction levels for landings, was intersted to know how they came up with these values,
Is it simulation and/or there is some analytical procedure to calculate them?
thanks
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Is it simulation and/or there is some analytical procedure to calculate them?
The analytical process of what limit the aircraft SHOULD be capable of takes place in the Design Engineer's office.
Test pilots must then DEMONSTRATE, in actual Cross-Wind conditions that the aircraft is capable of meeting the demands of the actual Cross-Wind during the test.
If, for example, the aircraft was capable of a 40 Kt Cross-Wind in theory, but the most that the Test Pilot could find was 35 Kt, the AFM would state "Maximum Demonstrated Cross-Wind = 35 Knots". (Seen that statement before?)
Regards,
Old Smokey
The analytical process of what limit the aircraft SHOULD be capable of takes place in the Design Engineer's office.
Test pilots must then DEMONSTRATE, in actual Cross-Wind conditions that the aircraft is capable of meeting the demands of the actual Cross-Wind during the test.
If, for example, the aircraft was capable of a 40 Kt Cross-Wind in theory, but the most that the Test Pilot could find was 35 Kt, the AFM would state "Maximum Demonstrated Cross-Wind = 35 Knots". (Seen that statement before?)
Regards,
Old Smokey
Which creates a potential dilemma for the pilot because it is not a limitation. So wise companies then create their own limits and publish them for all to respect and obey. They may use the demonstrated figure as the upper limit on a dry runway and will usually set lower limits for wet and slippery runways. The unwise leave it open and may even suggest that it could be exceeded - which technically it can because it is not a limitation. But of course while they may be unwise in dispensing such advice, they are usually wise enough to not put anything in writing.
I recall the dry crosswind 'demonstration' for the DC3 was 17 knots but at a couple of airports we regularly exceeded it and got away with it. I can now see that had I NOT got away with it it would have been: "Your Honour, how did Capt Mach arrive at the conclusion that he was better than the test pilot?" And would the Insurers pay? Hell, no.
I recall the dry crosswind 'demonstration' for the DC3 was 17 knots but at a couple of airports we regularly exceeded it and got away with it. I can now see that had I NOT got away with it it would have been: "Your Honour, how did Capt Mach arrive at the conclusion that he was better than the test pilot?" And would the Insurers pay? Hell, no.
The certification requirements (AFM) for cross wind landings are given in CS 25 Large Aircraft AMC 25.1581 6 3 (G) (about page 648)
As above, the manufacturer’s tests determine either the maximum demonstrated crosswind - not limiting (but unknown handling qualities in higher crosswinds), or where determined a limiting value, which is published in the limitations section of the AFM.
Generally, the certification tests are conducted on dry runways. Tests could be conducted on different runway surfaces (friction), but this creates problems in relating the test data with the vast range of conditions likely to be encountered in daily operations.
The effect of reduced runway friction can be calculated, but again crews’ rarely have runway condition data with sufficient accuracy. As an example, see MTED Approach and Landing slide 26, which shows a range of friction values for a grooved / non-grooved wet runway. In addition to this, the calculations (and reports to the crew) would have to consider runway texture, contaminant type and depth, amongst many other variables.
An example of the complexity (although a good solution) is given in Transport Canada AIM/AIR, see Table 3 which links crosswind with friction via CRFI, which IIRC, is not used outside Canada.
Thus, a general ‘operational’ solution is often used and the responsibility for this is with the operator / crew. Be very cautious of a crosswind on wet runway; heed the variability in wind reporting – see refs below.
Notes on crosswind landings from Boeing presentation:-
“Boeing publishes takeoff and landing crosswind guidelines in the Flight Crew Training Manuals
– Derived from analysis and piloted simulations
– Based on steady winds
– Function of runway condition
– Accounts for asymmetric reverse thrust
– Provides guidance on technique (side slip, crab)”
Runway Condition / Crosswind - Kts
Dry 40
Wet 25
Standing Water/Slush 15
Snow – No Melting 20
Ice – No Melting 15
(IMHO rather optimistic values)
See
ALAR Tool Kit Guidance Chap 8.7, also 8.5, and 8.6
IIRC this info is in general that used by Airbus, but their advice is also in Landing Techniques – Crosswind Landings.
Refs:
Crosswind - positon paper.
Crosswind Certification - How does it affect you?
Safety aspects of aircraft operations in crosswind.
Safety aspects of aircraft performance on wet and contaminated runways.
STAR 004
As above, the manufacturer’s tests determine either the maximum demonstrated crosswind - not limiting (but unknown handling qualities in higher crosswinds), or where determined a limiting value, which is published in the limitations section of the AFM.
Generally, the certification tests are conducted on dry runways. Tests could be conducted on different runway surfaces (friction), but this creates problems in relating the test data with the vast range of conditions likely to be encountered in daily operations.
The effect of reduced runway friction can be calculated, but again crews’ rarely have runway condition data with sufficient accuracy. As an example, see MTED Approach and Landing slide 26, which shows a range of friction values for a grooved / non-grooved wet runway. In addition to this, the calculations (and reports to the crew) would have to consider runway texture, contaminant type and depth, amongst many other variables.
An example of the complexity (although a good solution) is given in Transport Canada AIM/AIR, see Table 3 which links crosswind with friction via CRFI, which IIRC, is not used outside Canada.
Thus, a general ‘operational’ solution is often used and the responsibility for this is with the operator / crew. Be very cautious of a crosswind on wet runway; heed the variability in wind reporting – see refs below.
Notes on crosswind landings from Boeing presentation:-
“Boeing publishes takeoff and landing crosswind guidelines in the Flight Crew Training Manuals
– Derived from analysis and piloted simulations
– Based on steady winds
– Function of runway condition
– Accounts for asymmetric reverse thrust
– Provides guidance on technique (side slip, crab)”
Runway Condition / Crosswind - Kts
Dry 40
Wet 25
Standing Water/Slush 15
Snow – No Melting 20
Ice – No Melting 15
(IMHO rather optimistic values)
See
ALAR Tool Kit Guidance Chap 8.7, also 8.5, and 8.6
IIRC this info is in general that used by Airbus, but their advice is also in Landing Techniques – Crosswind Landings.
Refs:
Crosswind - positon paper.
Crosswind Certification - How does it affect you?
Safety aspects of aircraft operations in crosswind.
Safety aspects of aircraft performance on wet and contaminated runways.
STAR 004
