A320 landing distance without failure
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A320 landing distance without failure
Hello, folks!
While going through QRH the other day, I realized that the second note seems a bit strange for "LANDING DISTANCE WITHOUT FAILURE" tables.
Each LANDING DISTANCE WITHOUT FAILURE table has two notes, one of which is related to WEIGHT CORRECTION;
For Dry runway,
(2) Weight correction: if CONF FULL, subtract 10ft per 1klb below 150klb.
For Good runway,
(2) Weight correction: if CONF FULL, subtract 20ft per 1klb below 150klb.
For Good to Medum runway
(2) Weight correction: if CONF FULL, subtract 20ft per 1klb below 150klb.
Let's say that we are using autobrake low with flaps full, then the reference distance is same for all three runway conditions mentioned above.
If you follow the aforementioned note, then Good to medium and
Good runways produce a shorter landing distance than Dry runway.
Dry runway is supposed to give us shorter landing distance than Good or Medium, or so my common sense tells me.
While going through QRH the other day, I realized that the second note seems a bit strange for "LANDING DISTANCE WITHOUT FAILURE" tables.
Each LANDING DISTANCE WITHOUT FAILURE table has two notes, one of which is related to WEIGHT CORRECTION;
For Dry runway,
(2) Weight correction: if CONF FULL, subtract 10ft per 1klb below 150klb.
For Good runway,
(2) Weight correction: if CONF FULL, subtract 20ft per 1klb below 150klb.
For Good to Medum runway
(2) Weight correction: if CONF FULL, subtract 20ft per 1klb below 150klb.
Let's say that we are using autobrake low with flaps full, then the reference distance is same for all three runway conditions mentioned above.
If you follow the aforementioned note, then Good to medium and
Good runways produce a shorter landing distance than Dry runway.
Dry runway is supposed to give us shorter landing distance than Good or Medium, or so my common sense tells me.
Last edited by simyoke; 10th Oct 2016 at 05:56.
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Let's do a rather simple arithmetic here.
Assuming all the parameters same for both dry and good to medium runways;
conf: full
auto brake: low
weight: 100000 lbs
spd: assume no speed increment is needed
alt: 0 ft
wind: no wind
temp: ISA
slope: 0
reverser: both are operative
Let's add or subtract as directed in the table ....
,which yields
5870 ft for dry runways
5350 ft for good to medium runways
To me, it seems counter intuitive.
Looking up GETTING GRIPS WITH A/C PERFORMANCE, One thing that I can think of is precipitation drag.
The major difference comes from the second note since GOOD TO MEDIUM runways let you subtract twice as much as DRY runways
for weights under 150000 lbs.
Assuming all the parameters same for both dry and good to medium runways;
conf: full
auto brake: low
weight: 100000 lbs
spd: assume no speed increment is needed
alt: 0 ft
wind: no wind
temp: ISA
slope: 0
reverser: both are operative
Let's add or subtract as directed in the table ....
,which yields
5870 ft for dry runways
5350 ft for good to medium runways
To me, it seems counter intuitive.
Looking up GETTING GRIPS WITH A/C PERFORMANCE, One thing that I can think of is precipitation drag.
The major difference comes from the second note since GOOD TO MEDIUM runways let you subtract twice as much as DRY runways
for weights under 150000 lbs.
Last edited by simyoke; 9th Oct 2016 at 13:55.
Only half a speed-brake
Reverser is not taken into account (regulatory requirement) on dry runways.
The delay after touchdown before the autobrake LO comes into operation and the effect of the reverser in the meantime should explain the difference.
Also. you need to apply, I think, DRY/WET check, which tells you to disregard any wet runway results if they come to a better figure than those calculated from dry.
As far as I remember airframe drag (from spray) only enters the equation on contaminated runways.
The delay after touchdown before the autobrake LO comes into operation and the effect of the reverser in the meantime should explain the difference.
Also. you need to apply, I think, DRY/WET check, which tells you to disregard any wet runway results if they come to a better figure than those calculated from dry.
As far as I remember airframe drag (from spray) only enters the equation on contaminated runways.
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[QUOTE=FlightDetent;9535569]Reverser is not taken into account (regulatory requirement) on dry runways.
But when you do the landing distance calculation the table has reverser column.
[QUOTE=FlightDetent;9535569]Also. you need to apply, I think, DRY/WET check, which tells you to disregard any wet runway results if they come to a better figure than those calculated from dry.
DRY/WET CHECK is done for take off performance as the FCOM says in the take off performance section due to 15 foot vs. 30 foot screen height for dry runways.
QRH does not say doing dry/wet check for landing distance calculation, though.
But when you do the landing distance calculation the table has reverser column.
[QUOTE=FlightDetent;9535569]Also. you need to apply, I think, DRY/WET check, which tells you to disregard any wet runway results if they come to a better figure than those calculated from dry.
DRY/WET CHECK is done for take off performance as the FCOM says in the take off performance section due to 15 foot vs. 30 foot screen height for dry runways.
QRH does not say doing dry/wet check for landing distance calculation, though.
Last edited by simyoke; 10th Oct 2016 at 05:54.
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it just doesn't make much sense to me at all.
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I've just checked with A320 FlySmart EFB (Ipad).
The results with autobrake for dry, good, good to medium are similar. but from medium the Ldg distances start to increase.
The results without autobrake, the Ldg distance increases conventionally. (dry Ldg distance is shorter that good, good is shorter than good to medium etc...)
My guess: the autobrake system (the decel rate feature) is fantastic, it can cope pretty well with slightly degraded rwy conditions.
The results with autobrake for dry, good, good to medium are similar. but from medium the Ldg distances start to increase.
The results without autobrake, the Ldg distance increases conventionally. (dry Ldg distance is shorter that good, good is shorter than good to medium etc...)
My guess: the autobrake system (the decel rate feature) is fantastic, it can cope pretty well with slightly degraded rwy conditions.
Last edited by Feather44; 10th Oct 2016 at 18:21.
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Yes that is when max manual braking is used, however, max manual braking is rarely used and when you put in the parameters that are given as above for landing distance calculation, it would look at least a bit strange mainly beacause of weight correction factor being twice as much for runways with less friction.
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weight correction factor being twice as much for runways with less friction.
FlightDetent explained in post #5.
You are not simply comparing only the effect of brakes and runway friction.
Autobrake Low simply sets a deceleration rate which might be achieved initially with reverse thrust and the brakes hardly doing any work.
If the published Landing Distances assume no reverse credit on a dry runway but use of reverse on the others, then your observations make sense.
See https://www.fly19.net/wp-content/upl...erformance.pdf
Last edited by Goldenrivett; 11th Oct 2016 at 11:24. Reason: typo & Link
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It's not friction causing the difference - it is reverse credit.
FlightDetent explained in post #5.
You are not simply comparing only the effect of brakes and runway friction.
Autobrake Low simply sets a deceleration rate which might be achieved initially with reverse thrust and the brakes hardly doing any work.
If the published Landing Distances assume no reverse credit on a dry runway but use of reverse on the others, then your observations make sense.
See https://www.fly19.net/wp-content/upl...erformance.pdf
FlightDetent explained in post #5.
You are not simply comparing only the effect of brakes and runway friction.
Autobrake Low simply sets a deceleration rate which might be achieved initially with reverse thrust and the brakes hardly doing any work.
If the published Landing Distances assume no reverse credit on a dry runway but use of reverse on the others, then your observations make sense.
See https://www.fly19.net/wp-content/upl...erformance.pdf
You might want to look up the landing distance tables contained in QRH which can be found in the link you provided.
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You might want to look up the landing distance tables contained in QRH which can be found in the link you provided.
Weight 66Tons Autobrake Low, No Rev
Dry Ref Dist = 1950m Correction -10m/Ton below 66Tons.
Good Medium Ref Dist = 1960m Correction -10m/Ton below 66Tons.
Medium Ref Dist = 2140m Correction -20m/Ton below 66Tons.
Poor Ref Dist = 3540m Correction -30m/Ton below 66Tons.
The bigger corrections / Ton below 66 Tons for Medium - Poor conditions will be due to Airframe drag etc. which has a longer time to produce an effect due to the longer Landing Distance.
I suspect your figures have a printing error.
