Manual Landing VS Autoland performance

[lion-g]

Hi Guys,

Was just wondering if there's any writeup on the performance calculation on this topic. The landing distance required for autoland is higher than manual landing with SAME autobrakes setting.

From my understanding, autoland takes into consideration the flare height at 40ft AGL while manual landing is assumed to be 50ft above threshold and touchdown at 1000ft marker.

IS this correct ?

Need some explanation from the experts out there.

Cheers,
Liong

[411A]

Depends on the specific airplane.
With the first CATIIIB certificated widebody jet transport, the L1011, the autoland flare maneuver begins at 50 feet, and will normally provide a very accurate touchdown reference....every time.
If auto brakes are used (-500 model) the absolute shortest possible landing distance can be achieved.
It is an extremely accurate dual/dual system and was the first of it's kind on a widebody airplane.
According to the production test pilots I spoke to years ago, the autoland system on the L1011, combined with autobrakes, could consistantly achieve superior results, versus the normal line pilot.

[lion-g]

HI ,

Yes Sir, I totally agree with you, statistically, Autoland will perform better than pilots in term of accuracy. But what's bugging me is the required landing distance for autoland is longer than manual landing.

Somebody suggested that it's due to the fact that autoland landing distance calculates touchdown point at 2500ft rather than 1000ft in manual landing.

Any help on this will be much appreciated.

Thanks

[Mad (Flt) Scientist]

Hi Guys,

Was just wondering if there's any writeup on the performance calculation on this topic. The landing distance required for autoland is higher than manual landing with SAME autobrakes setting.

From my understanding, autoland takes into consideration the flare height at 40ft AGL while manual landing is assumed to be 50ft above threshold and touchdown at 1000ft marker.

IS this correct ?

I would guess - and caution that this is a guess - that the difference may come from the different philosophies which one is (sometimes) forced to assume when dealing with automated systems as opposed to pilots.

Although we all know that humans are fallible, one can assume for the purposes of certification that a given procedure is followed appropriately (once it's first been shown to be a practical procedure, of course). Therefore the manual landing data can be derived from the performance testing, conducted 100% by the book, no procedural errors considered.

Yet when we consider the performance off a system, we often have to consider error build-up within that system. As a result, the quoted distances for the autoland may represent the autoland system "on a bad day" whereas the manual data is for the nominal case.

[411A]

Yet when we consider the performance off a system, we often have to consider error build-up within that system. As a result, the quoted distances for the autoland may represent the autoland system "on a bad day" whereas the manual data is for the nominal case.
I would totally agree.
Now, some pilots might like to think that they can 'out smart' a well designed dual/dual automatic approach/land (autoland) system, however...many of these same pilots will try a slight 'duck-under' maneuver, to achieve short landing distances.
This is a very BAD idea, with a large wide-body airplane.
Specific threshold crossing heights are mandated with these specific aircraft (IE: standard body L1011, 42 feet, minimum) and if you might try the slight duck-under 'maneuver', the landing gear might well become inter-mixed in the approach lights frangible bits.

Rest assured...this will not impress the respective fleet manager.

Beware, large wide-body airplanes need extra caution, make NO mistake.

PS:
I would be totally remiss if I did not mention the HS.121 Trident...the first to achieve complete all-weather triplex autolanding capability.
Full marks for these folks.
IE: they did it first...others followed.

Superb results...absolutely.

[ElNino]

Manual landing figures based on threshold speed of Vls. Autoland figures based on threshold speed of Vls + autothrust increment (5kts).

[jb5000]

The A320 approach speed is 5 knots faster if autothrust is being used, or if an autoland is being performed. (Vls + 5 as opposed to Vls).

Clearly, this would have an effect on the actual landing distance.

Hope that's of interest.

[The Real Slim Shady]

Autoland certification has to allow for a scatter effect: that is the touchdown points will not be consistent. This can be due to weather, runway, terrain or fleet mean average.

Thus the Authority will take the worst case and that will become the factor applied to an autoland as the increment.

[boeing_bananas]

Hi,

Our performance manual contains figures for both manual and autolands. There is note that states that the landing distance at a given weight is greater for an autoland than a manual landing due to a possible longer flare. The actual increase depends on glideslope angle and a/c height over the threshold.

Although as has been stated above, in practical terms it seems to do a pretty good job - as indeed it should!

Also there is a note saying that on CAT2/3 runways there is a lower go-around WAT limiting temperature for a CAT1 autoland due to a more restrictive go-around requirement. I'm not sure what that requirement is tho.

Hope that helps.

[Iceman49]

jb5000 jb5000 The A320 approach speed is 5 knots faster if autothrust is being used, or if an autoland is being performed. (Vls + 5 as opposed to Vls).

Clearly, this would have an effect on the actual landing distance.

Hope that's of interest. ]

Isn't the approach speed 5 knots faster than Vls...whether or not a/t is used, are you saying you are flying the approach at Vls?

[NSEU]

From my understanding, autoland takes into consideration the flare height at 40ft AGL while manual landing is assumed to be 50ft above threshold and touchdown at 1000ft marker.

The 747-400 flare height is variable depending on V/S during approach. The system aims for 450 feet past the Glideslope Transmitter with a touchdown rate of 1.5 feet/sec.

Where do you usually land your aircraft? :)

Rgds.
NSEU

[lion-g]

Hi guys,

From Boeing point of view, we will fly Vref + 5 kts all the way down until flare height which we aim to fly over the threhold at Vref and touchdown at 1000ft marker. (Manual landing). As for autoland, the system will still fly Vref + 5 till flare height of 40ft AGL which i suppose, over the threhold.

I can't seems to find any write up on autoland performance from my side and I would appreciate if you guys can provide me with references from ICAO recommendations on autoland performances or any other authority writeup ould be nice.

Thanks a lot for your input and discussion.

Cheers,
lion-g

[capt_akun]

Hi.

What's the 'duck-under' maneuver?

if you ducking under on approach, doesn't that make you approaching flat? As a result, you have a higher forward momentum then a normal approach which may results in longer landing distance?

[Old Smokey]

Lion-g,

Just to clarify a point or two, you state "As for autoland, the system will still fly Vref + 5 till flare height of 40ft AGL which i suppose, over the threhold.
". If you're referring to B777 (I'm guessing), flare height is indeed 40 feet, but Threshold Height is still 50 feet, thus, the flare begins after the threshold.

Again, assuming that you refer to B777, you would be aware from experience that a flare commenced at 40 feet for a manual landing would result in landing "deep", 30 feet (and less for braver souls) produces the most consistent touch-down at the 300M marker, thus, the 40 foot flare will be deep, requiring a longer landing distance.

Not a very scientific answer, but it may supply your answer sought.

Regards,

Old Smokey

[Aztec Kid]

An excellent publication by Airbus, “Getting to Grips with Aircraft Performance”, has a section explaining how landing distances are calculated for both manual and automatic landings. The landing distance is greater for automatic landings since there are additives related to the demonstrated mean touchdown point. Another factor, which was mentioned in earlier posts, is the approach target speed of VLS+5 at 50 feet (with the autothrust on).

I honestly believe that the published figures for landing distance for an automatic landing would be a more realistic assessment of required landing distance than the numbers for the certified actual landing distance for manual landings. The calculations for manual landing distance are based on a speed of VLS at 50, touching down with no float, and application of maximum braking force.

While this does provide an accepted standard for comparing aircraft from various manufacturers, it is not how transport aircraft are typically flown in passenger operations. Even an experienced passenger would be frightened if a pilot used the techniques employed during landing certification tests.

I have included a link to a video of a manually flown landing accomplished during certification testing of the DC-9-80. This video is a graphic example of how aggressive the test pilots can be, when attempting to minimize the demonstrated landing distance.

I hope you find this helpful.

The Kid

Getting to Grips with Aircraft Performance
SmartCockpit - Airline training guides, Aviation, Operations, Safety (http://www.smartcockpit.com/pdf/flightops/aerodynamics/18)

DC-9-80 Landing Certification Accident Video
YouTube - McDonnell Douglas MD-80 Crash Landing (http://www.youtube.com/watch?v=jaqRx3SV-k8)

NTSB Accident Report AAR-82-2 DC-9-80 Edwards Air Force Base
http://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR82-02.pdf

[ALK A343]

Good point Aztec Kid, it is in fact more realistic to use the autoland landing distances with autobrake. Actually Airbus recommends this in the FCTM in case of an enroute diversion to assess the suitability of an airfield.

[lion-g]

Hi all,

Thanks for the reply. I have flipped through the write-up on performance and it's seems that it will be written in the AFM should the autoland landing distance be more than the manual landing landing distance.

I have flipped through the AFM for BOEING aircrafts and nothing mentioned. Can those on the BOEING a/c highlight this to me ?

Or can i assume the charts given is catered for autoland ? (BOEING)

Airbus reallys provides good writeup and I suppose Boeing will have similar writeup somewhere.

Thanks again for all your inputs really appreciate it, learnt a lot from you guys.

Cheers,
lion-g

[FlightDetent]

Isn't the approach speed 5 knots faster than Vls...whether or not a/t is used, are you saying you are flying the approach at Vls? You could. The +5 kt increment to Vref to calculate Vapp by FMS is added because it is assumed A/THR will be used. If you don't and calculate Vapp manually with 0 headwind you should find out that Vapp = Vref + 0 = Vls.

FD (the un-real)

[B737NG]

Ducking under is going under the Glide Slope / VASI to hit the ground asap. 411A is right You might be able to do that on a Baby-Boeing but you will get cought if you try to cheat in a B747, B767 or B777. Same for the Busses: 320 You might walk away with it but A330 + A340 you can scratch the Undercarriage into the Metal before the concrete.

Our QRH, PI section, Company tailored, states + 2.500 feet required Landing distance for Autoland when You calculate the "numbers" for the Landing.

I hope that helped you. For more details required ask the manufacturer.

Fly safe and land happy

NG