BASIL said
Ref heavy braking producing a nose-down pitching moment; isn't this thread about landing on more or less slippery runways where heavy braking would be impossible?
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To re-cover old ground:
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a. the CofG accords a basic nose-down weight distribution (ie. before any retardation cuts in)
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b. even minimally achieved braking will increase that (and reverse certainly will). At speed, spoilers will be helping greatly to get weight onto the wheels. However on contaminated runways a bow-wave of water/slush under the leading-edge of each tyre still tends to oppose wheel rotation (think of that as
hydrodynamic lift)
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c. However as RATHERbeFLYING pointed out,
<<The autobrake demands whatever braking it takes to achieve a deceleration rate (and can do that as long as the wheels keep spinning) - otherwise anti-skid prevails (and the called-for rate is unachievable. That is why it is important to prevent the wheels from locking.>> So what we must try to do is to increase the weight-on-wheels to a maximum. In MANUAL braking, if you don't stop the wheels, you won't blow the tyres. Under AUTOBraking it's a matter of reducing the intervention of anti-skid - which stops you from blowing tyres but won't assist more effective braking. That can only be done by maximizing the rotational traction of the tyres. Progressive backstick (i.e. UP elevator) works well against the distant nose-gear fulcrum to lever the main-gear INTO the deck, increasing that weight on the main-gear wheels.
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That it works like that is undeniable. Unfortunately the level of disbelief and denial seems to be built-in ("why, if this is so, is it only now being revealed?"). Well I used to teach and demonstrate it and wrote it into a few syllabi... but many a lost art has become irretrievably lost over time. Also firmly ensconced in the psyche is the belief that any minor variation from a strictly specified (but mostly imaginary) modus operandi means instant disaster. However if you read the two cited manufacturers' documents (one's a powerpoint and one's a pdf, referenced in earlier links), you will note that both Boeing and Airbus are emphatic that effective braking in the muck relies upon getting the weight off the wings and onto the wheels. It is indeed unfortunate that the handling technique of
progressive backstick braking has become a lost art. If it hadn't, I'm sure that many, if not most, marginal (short) contaminated runway overruns might have been avoidable.
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Of course it's something that needs to be introduced soon after spoilers are up and nosegear is down, as obviously the elevator authority will diminish with speed loss.