The B737-200/400 has a +or- 2% runway slope limit. Why? Surely if one wanted to take off with an upslope of greater than 2% you would just then have to incur a severly restricted take off weight.Going down hill helps I thought? Tail strike perhapes on a severe downhill in the -400 but what about the -200? Anyone have any ideas?
As shown in the attached extract from AC25-7A, the FAA's Flight test Guide for Part 25 certification, presentation of data outside the +/-2% slope band requires additional work by the OEM. Unless they need to do that for a (significant) sale, they won't.
OK, that didn't work
You'll have to take my word for it, then! Or check the AC, it's in chapter 8 of the Ac (Airworthiness), section 230.
All JAR/FAR-25 aircraft have this limitation. A runway with greater slope than 2% is no place to be operating an airliner ;-) It would give severe penalties for t/o & ldg (balanced field length aso). You're right about the possibility of restricting TOM / LM, but then you wouldn't be making any money!
Interesting photo. Air Niugini operate F28s into airports with about 5-6% slope. Naturally and legally there has to be a V1 for them but there is a slope above which very diminishing stopping performance is returned for aircraft above 5700kg.
Operations in aircraft below 5700kg are routinely performed in PNG at strips up to 17.5% slope. Indeed you are are committed as soon as you open the throttles at very steep strips but have no performance guarantee. The best I could teach pilots to do was; In the event of an engine failure, reduce the thrust on the operating engine to preserve directional control and then introduce it as you accelerated and then drifted or fell off the end of the strip.
At very steep (above 12% say) strips you were much safer as the natural acceleration of the aircraft with gravity meant that even with an engine failure and reduced thrust on the other engine it was highly likely that you would achieve flying speed as you pitched forward off the end of the strip. The steeper the strip also increased the likelyhood of a big dropoff and deep valley at the end of the strip.
Now that I fly 737s it amazing the number of pilots that have problems with airports that have 1% slope and the number of hard landings that are recorded as a result!!!!!
Like mad says, its all about money. You can go to Boeing and ask for 3% but it will coat you. Not many airports aroung the world where you operate airliners above the value of 2% so this was probably the cut off value. To do extra flight testing to get the a/c cert for 3% for a handful of airports where nobody goes anyway would have been expensive.
An interesting comparesen was the gravel kit for the 737-2, an afterthought for one operator initially I believe. In the process of flight testing and getting certification for this I was told about 10 engines were distroyed.
To complicate the issue, I was under the impression that slope was measured as a difference in elevation between runway ends. Thus there could be a slope much greater than 2% from the threshold to say runway midzone. Or is it considered that this all balances out in the end?
The dash 7 and beaver are living proof that the canooks build the best airplanes..and brew the best beer as well....best ride of my life was on a rocky mountain dhc-7 into steamboat colorado.. what a glidepath!!! no not hayden where the normal guys go...the real steamboat springs!!
Its up to the airline to decide what slope it wants to use, we generally go for the easy option of taking the runway end elevations divided by the runway length. But in certain cases where we know that the runway dips in the middle and that the slope on the accelerate go portion is greater than the average, i.e Manila, we just use the maximum slope.
The penalty for doing this on a B747 is around 3000 kgs, but is a lot less costly than putting the aircraft off the end of the runway.