demonstrated crosswind and restriction at a specific airport

[Journey Man]

Recently operated into LIMJ and was surprised to read in the briefing notes that crosswind is restricted to 70% of the maximum demonstrated crosswind from the AFM.

Seemed fairly unusual, especially considering this is the maximum demonstrated crosswind… Anyone come across this elsewhere?

[Journey Man]

Hmmm.. not sure which question you're replying to. I know where it was for that field as stated. And, after briefing the field pre-trip, I understand why.

My query focusses on the restriction being based on the demonstrated cross wind limitation. Demonstrated and maximum crosswind limitations have subtle differences.

[TopBunk]

I used to operate in there quite regularly about 20 years ago in a B737-200.

As the notes I have seen:

"5. WIND LIMITATIONS
5.1 A 30% reduction from maximum demonstrated crosswind component as published on the AFM (Aircraft Flight Manual) shall be applied for each type of aircraft. The above values shall be lowerthan the lowest values published on the Approach Plates and/or any other values published.
5.2 AD occasionally affected by terrain-induced wind shear phenomena, mostly associated with winds having a 330°-060° direction and 10-20kt intensity and more often occurring between November and April. The daily distribution shows a peak between 8pm and 10pm."

I can confirm that on several occasions on final approach all was peaceful, calm and smooth until about 7 or 800ft when all hell broke loose when the katabatic wind hit us. Wind from calm one second to a very turbulent NNw varying to NEasterly at 25-30 knots giving interesting flight path and flight control inputs required. My advice would be to take the restrictions to the limits very seriously and be prepared!

Other notable airfields with limitations are Gibralter and Funchal although I haven't operated in/out of them. I would also suggest that Narita can be challenging - witness the various incidents there.

[Journey Man]

I haven't discounted the limitation imposed at the airfield, or the significance of it. TopBunk, thank you for your experiences operating into LIMJ.

With the varying methodology used in demonstrating crosswind components, in particular with reference to gusts, it seems strange to apportion such emphasis to the demonstrated crosswind limitation when, despite what LookingForAJob says, the regulating authorities approve the OMs, and therefore OM limitations are a known quantity. Furthermore, the demonstrated crosswind limitation, as usually presented in an AFM, is much less a known quantity than is being alluded to in this thread without conducting further investigation into the manufacturer's methodology for demonstrating the crosswinds - again drawing your attention to the example of gusts - which should be the basis for publishing actual specific limitations in the company OM-B limitations section.

Hence querying this as to why the same restriction isn't made based on a 30% reduction in operator's type specific crosswind limitations and below any maximum crosswind limit published on the approach plate.

[safetypee]

If a crosswind operation was been found to be limiting by the manufacturer then this will be published in the AFM as a ‘limit’.
Max demonstrated crosswind is not limiting, but very good advice. The value is normally published by the manufacturer in the crew operating manual. The value implies that a limit has not be encountered, but does not indicate what the margin from any limit might be, i.e. treat it as a limit. Also the wording and advice on gusts can vary.
In both cases, good safety practice recommends that operators and crews set their own lower limits according experience and situation.

Thus whilst the intent of the LIMJ statement is reasonably clear, the terminology used might be confusing. With local knowledge, operators would be expected to use a lower limit; however visitors would more likely depend on published warnings often given as a ‘cautionary’ statement. The advantage of the LIMJ ‘limitation’ is to put more emphasis on the hazard and encourage operators to reduce crosswind limits more than they might consider.
In addition, operators must consider the effects of a wet or contaminated runway where even greater reductions in crosswind should be applied, as with gusts.

A descriptive wording of a hazard is open to interpretation due to variable human performance; setting a ‘limit’ provides a strong marker-point on which to base judgement. Thus the LIMJ 'limit' is a good safety communication, it could be worded more consistently with aircraft / operational documentation.

[Journey Man]

I agree there is a lot of ambiguity with the demonstrated crosswind limitations from the AFM. I believe after the Lufthansa wingtip strike in strong crosswinds, it was recommended that certifying authorities standardise the demonstrated crosswind testing protocol.

In hindsight, private operations may only have an AFM for guidance and hence the only guidance on limiting crosswind conditions available to such pilots would be the AFM defined maximum demonstrated crosswind. For commercial operations, the Ops Manual should be definitive, and hence removes any ambiguity. As I understand CAP789, commercial operators are obliged to define crosswind limitations, although discussions with colleagues in numerous operators yields differing understandings off this. I may well have misinterpreted this.

CAP 789

4 Crosswind Limits for Take-off and Landing

4.1 It is not sufficient to repeat a statement in an AFM that a particular crosswind component has been found to be acceptable; operators' limitations should be stated in unequivocal terms and account taken of the effect of gusts and surface conditions. Limits in excess of any figure mentioned in the AFM will not be acceptable. In addition, consideration should be given to any reduction in limits due to narrow runways.

[BOAC]

I assume the LIMJ 'limit' is due to the narrowness of the runway side shoulders at the north-west end, and setting it on max dem'd x-wind' rather than a specific knottage avoids exceeding what might be a low airframe x-wind limit.