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Hi,
Can anyone tell me the autobrake setting assumed for the airfield specific (ie not the QRH) 737 landing performance charts.
On a typically flat runway , calm winds at sea level I get just under 78 Tonnes for a wet runway. Specifies anti skid,thrust reverser etc but no mention of the autobrake setting.
:confused:
Depending on the program in use, the likely answer is Maximum Manual Braking.
Mutt
I suspect it has to be an autobrake setting as maximum manual braking would be a variable. Airbus did some tests on the A340 to check maximum manual braking against max auto brake and the auto brake won every time. Reason was primarily that pilots could not consistently keep maximum brake applied throughout the deceleration. Although Boeing do say max manual is going to stop you in a shorter distance (so it is different to Airbus in this respect) I am not sure they would put something which is variable as the landing performance datum.
Generally as its AFM Approved Data, Maximum Manual Braking is used as per the FAA certification requirements.
Mutt
OK Mutt thanks for the info. Can see the point of having the shortest distance the aircraft is capable of....just think it should be stated in the pre amble.Many people will base their performance on something other than max manual which is most uncomfortable for pax. Potential for an overrun at places like ABZ.
In my experience the Runway specific 'MLM' to which I assume you refer normally well exceeds the a/c MLM and I would expect crews who had ANY doubts about roll-out to check the QRP weight/autobrake LDR table to determine what they needed. Only in a few places has this not been so - eg R27/wet at JSY, and there we always looked at the QRP if in doubt. AFAIK the figures to which you refer are primarily for planning purposes?
Which runway/type did your post #1 refer to?
Kit d'Rection KG
25th Oct 2007, 20:03
I suspect it has to be an autobrake setting as maximum manual braking would be a variable
RMC, I'd be most gratified if you'd either (a) reassure me you're not a professional pilot, or, (b) explain why you think that maximum manual (should be pedal) braking is variable. It means pedals to the mechanical stops, usually before touchdown in certification flight testing. Thus system pressure goes to the anti-skid units, and brand new tyres and so on do the rest.
john_tullamarine
25th Oct 2007, 22:19
(a) Many people will base their performance on something other than max manual
think we might be confusing certification with "routine" operational performance. For certification .. and maximum braking means just that .. the landing is somewhere between terrifying and horrifying. For routine (ie typical pilot, etc) the 1.67 factor gives you a fair bit of room with which to play in looking at the AFM. For everyday operations, we normally have a variable amount of additional fat in that the runway is longer than the AFM scheduled requirement.
(b) usually before touchdown
perhaps just after touchdown .. but nonetheless impressive if one is on the aeroplane at the time ...
Kit I am a professional pilot now but used to be a systems test engineer. Spent several months testing brake performance and can assure you that maximum manual braking IS variable. Whilst my involvement was not restricted to the A340 test I described it best illustrates the issue. They had four test pilots one of them did not apply max braking from the start (as it felt so severe)...non of the other three were able to maintain max braking until the stop. A combination of trying to keep the aircraft straight whilst apply full leg pressure and leg fatigue during the deceleration. The aircraft beat all four pilots (when it came to a stop tyres deflated). Maybe before you start patronising you should give others a little credit.BTW the pedals go nowhere near the stops when max foot pressure is applied.
BOAC think I used GLA 23 wet for the performance. As you say it is normally above max landing weight ...it is the overweight return case which raised this question. I would of course look at the QRH but the assumptions are different from the perf manual.
it is the overweight return case which raised this question.
This shouldnt be a factor, from the performance aspect, if you can takeoff on a runway, you can return to land on it. You dont even have to look at the QRH as the calculation is already done in the takeoff analysis.
Mutt
As Mutt says, Boeing state that if you can take-off you can land at F30 or F40, but they DO refer you to the QRH/P tables for autobrake which give LDRs up to max autobrake.
I can only refer to the 700, but at MTOM Boeing offer 1295mtrs for landing at F30 with max a/b.
Kit d'Rection KG
26th Oct 2007, 17:27
RMC,
I find your reply interesting. That one TP should not have been working on certification, IMHO.
Regarding mechanical stops, in all the transport aircraft (and, as there have been lots of them, simulators) I've flown, I have had no problems reaching definite mechanical stops on the brakes during RTOs. This includes the B737-NGs. It's something I check with care when I do it. I haven't flown the A340 (I did 'fly' the A340 simulator), but if it causes its pilots problems applying maximum pedal braking to a stop in the worst takeoff case, then there's a certification 'issue'. Blow me, a certification 'issue' on a big 'bus! There's a first!
John,
'Terrifying', 'horrifying' (your words) or 'awe-inspiring' (mine). It gives immense confidence to the pilot, who knows the stopping capabilities of his aircraft. These days it's often the stopping capabilities of the surface under the wheels that lets the whole thing down. High speed stopping is perhaps the most important respect in which simulators don't replicate the 'pilot experience'.
john_tullamarine
27th Oct 2007, 01:25
simulators don't replicate the 'pilot experience'
This is the main problem with sims ... how close is the box to reality (ie what is the fidelity). In the final analysis the only "true" simulator is the aeroplane .. all the ground based boxes are in error to a greater or lesser extent. For routine airline use, the simulator fidelity has to be "good enough" for the purpose but the reality is that, outside the operating regions tweaked for the purpose, the box might be VERY far from reality.
Most pilots never get a chance to participate in REAL performance limiting takeoff and landing trials .. I don't use my descriptors lightly .. first time I was involved (with an experienced OEM experimental TP driving) I nearly embarrassed myself ..... good fun but VERY different to normal line landings .. which is why I often suggest that pilots ought to respect the 1.67 factor for normal landings ..
Keep in mind that
(a) the test folk don't just head out to run some trials today because they had nothing much better to do .. the crew will have done a moderate series of practice runs over the previous days to make sure that the polish is well buffed
(b) on the day, the TP will nominate a number of trials to be discarded for whatever reason ...
(c) when we get to run the post trials analyses, we engineering folk toss out a few more which don't suit the purpose ..
(d) end result is the data presented is skewed somewhat toward the less conservative .. one of the reasons that the AFM fudge factors are required.
Thanks for the replies guys.
Kit wouldn't disagree with the TP comment. They used one from each of the four partner countries for this test (some kind of bottle competition). The English, German and French guys did apply max brake pressure (until their old legs let them down).