Many years ago the executive of the Oz aviation regulatory authority found that the then current runway width requirements for transport category aircraft were inhibiting growth opportunities for some sectors of the industry.
They directed both the flying operations and airworthiness branches to review the current standards and develop set of standards which would permit these aircraft to operate on “narrow” runways.
The overriding requirement was that the level of safety was maintained.
The airworthiness branch concluded that the only way to maintain the required safety level was to ensure, as far as possible, that the aircraft remained on the runway during both normal and abnormal operations. This required a review of all runway handling characteristics, and all MEL items which could adversely affect aircraft controllability.
This meant the aircraft must remain within the confines of the runway during:
1. Critical engine failure, with a continued takeoff at Vef min and maximum approved crosswind limit;
2. A refused takeoff as above; and,
3. A one engine inoperative approach and landing from a position significantly displaced from the runway centreline at about 500 feet on final approach.
This all required flight testing with the usual requirements for Vmcg tests, such as a calibrated weather station, means of measuring lateral deviation from the runway centre line, disconnecting nosewheel steering, and critical engine shutdown by turning the fuel off. In some cases a throttle chop was an acceptable means of compliance, provided there was a data correction method, approved by the original certification authority.
I carried out the flight testing of, IIRC, 10 aircraft types both jet and turboprop. This was done with company pilots in the RHS. The items which were non-issues were the refused takeoffs and asymmetric landings.
The big issue was staying on the runway during the continue takeoff.We developed a workup method which gave us a good feel for the sensitivity of aircraft handling, to reducing the crosswind component, or increasing Vef and hence V1. I don’t recollect any aircraft which would stay on the runway with a failure at Vmcg and maximum cross wind.
The operators were given the option of how to fit their aircraft with the runways they wished to use. For example if runway length was not limiting they could overspeed V1 and have a higher crosswind limit. For some aircraft a derate which reduced Vmcg may have been an option but I don’t think it was ever used.
This system is still used by Oz CASA, and anybody who Googles CASA Narrow Runway will find all the info. The A380 was limited to 65m runway until a successful narrow runway approval request resulted in clearance to 45m.The procedure was adopted fully or in part by some other regulatory authorities.
This thread is really about crosswind handling, and unfortunately I haven’t much to offer as I used the same techniques for all the aircraft I tested.
Takeoff: keep the wings comfortably close to level with minimum necessary lateral control input, rotation was a bit more difficult to sort out due to yawing moments from both the crosswind and engine asymmetry. But as the book says, all this should be easily accomplished by the average pilot.
The only landing technique used was to fly the approach with drift, during the flare use rudder to align with the centre line, when that stuffed up a bit of bank (within the near ground bank angle limits) and touch down on the upwind wheels.
During my involvement in this exercise I have flown literally hundreds of fuel off engine failures at speeds around Vmcg, with both zero crosswind (as required for Vmcg determination) and with up to limiting crosswinds as required for CASA runway width testing.
It is important to note that FAR part 25 Vmcg testing is a zero crosswind test, FAR part 25 crosswind testing is all engines operating. There is no part 25 certification requirement to blend the two issues, and you all may be operating aircraft which will depart the runway with the critical V1min engine failure. While FAR part 25 has a number of “catch all” paragraphs to weed out unsatisfactory characteristics which may be noticed but don’t have a specific requirement, they are yet to be used in this case. I imagine that the FAA standards development folk have a bunch of statisticians who claim this is ani extremely unlikely event, akin to a double failure, so no accountability necessary.
It should also be noted this was not an exercise in re-determination of Vmcg. The requirements for Vmcg are clearly spelled of in FAR part 25 and the test methods in AC 25- XX ie about 25-7d at the moment. Don`t forget to check the amendment status you are interested in as FAR part 25 Amendment 42 bought in a lot of changes including maximum permitted rudder forces and centreline deviation limits.
Some lessons:
Turboprops have much worse handling qualities than jets in these tests, also the undercarriage layout on many means that a wheel will depart the runway with less deviation than similar jets.
If you wish to get a feel for where your aircraft fits in the scheme of things, get the following information:
1. What was the certification basis? This will show if it is a zero wind Vmcg or a 7kt crosswind Vmcg.
2. What was the lateral deviation determined when Vmcg was tested, the lesser the better.
3. Was the limit pushed to achieve the minimum possible Vmcg to minimize takeoff distance requirements.
This has been put together quickly, from memory as I am far from home with no access to relevant documents.
This was a complicated, time consuming project and only the surface has been touched on. For example I have made no mention of the flying operations and airworthiness systems engineering staff inputs.
Last edited by zzuf; 7th Sep 2018 at 18:13.