Vmcg Techniques

[bayonette]

I was just wondering whether it is possible to conduct Vmcg testing on a standard runway with minimal risk? What are the techniques that are used to conduct these tests? Sorry , if these are too basic questions...if any one can explain in simple terms without jargons, it would be of help to me.http://static.pprune.org/images/smilies/eek.gif

[Mad (Flt) Scientist]

I was just wondering whether it is possible to conduct Vmcg testing on a standard runway with minimal risk? What are the techniques that are used to conduct these tests?

I'm glad to see you said "minimal risk" and not "no risk".

I'll answer a slightly different question; It is possible to conduct Vmcg tests on a standard runway with acceptable risk. But the risk will not be minimal - clearly there are issues associated with use of a standard width runway that can be resolved by use of a wider runway....

The technique used first is to assess the risk - risk management 101 - what could go wrong, how can we reduce the probability of it happening, and how can we reduce the hazard if it does happen. (Risk being, simplistically, the sum of the hazard*probability of all the possible events, reducing any of the three is desirable).

So, what could go wrong? The obvious is loss of directional control, resulting in runway excursion. Other issues could be runway overrun, and all the usual runway hazards. Let's focus mainly on the directional control issue, and apply the normal operational mitigations for the other stuff.

How do we reduce the probability of loss of directional control? We can:

Perform analytical predictions to understand the expected Vmcg to ensure we start the tests at a sensible value (and base those predictions on the most reliable data practical)
Conduct work-up tests to ensure we start at a safe condition where control is assured (and also use these tests to build familiarity for the next bullet)
Have crew familiar with the test technique - including all the test personnel, not just the pilot
Conduct the test in favourable conditions - dry runway, light (zero) winds
Use as wide a runway as available


How do we reduce the consequences of the excursion if it happens?

Ensure that the possible runway excursion zones are free of non-frangible objects (including other a/c!)
Also, no ditches or other hazards on the runway side!
Make sure CFR are present and briefed - including on the aircraft entry techniques, which may be unusual for a test a/c compared to normal a/c
Have flight crew wear safety equipment - helmets, fireproof suits, etc - but not parachutes!


I'm sure there's more, which leads to the final item. Don't rush anything! Review the test plan until everyone is happy, and take the time to make them happy. Don't be afraid to scrub the test if the weather goes pear shaped. Do it right, because doing it wrong will result in many more delays.

[ICT_SLB]

A further clarification of risk reduction is to require no vehicles within 400 feet of the runway centerline. This includes CFR and photographic!

It wasn't Vmcg but during water trough testing that a well-known biz jet departed the runway and clipped a photographer's truck that was parked too close. Not only loss of the airframe but nearly three fatalities as well - thank goodness for oversized astronaut's boots!