hello ba 146-100,
flaps40 & flaps 30 are both boeing certified normal landing flap configurations. because flap40 generates more lift & a lot more drag, technically the difference is a lower vref( about 4 a 5 knots) for a flap 40 landing resulting in a shorter landing roll. the "price" to pay as nothing in this world is for free, is higher thrust settings on approach, resulting in higher fuelflows & more noise.
your question was: the choise between flap30 & flap40?
it is the captains decision & in accord with company policy:eg,
"preferential landing flaps setting is flap30".(low drag, low noise, lower fuel consumption, the company likes this last assumption)
"flaps40 may be selected for a landing distance available(lda) of 7000ft or less".
"flaps40 is mandatory for an lda of 6000ft or less( is considered a short field)".
"flaps40 is recommended for cat2/3 ( lower deck angle)".
other considerations may include landing weight & runway status, dry, wet or contaminated. it is good operating practice to discuss landing flap setting during the approach briefing, so both pilots agree. i totally agree with captain marvellous summary.hope this answers your question?
Last edited by blackmail; 28th November 2004 at 13:37.