Page 1 of 1

Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 5:33 am
by themathguy
Hello! I have a question about landing distance and go-arounds. I understand that airliners have calculated landing distances associated with factors such as weight, flaps settings, runway contamination, etc. Additionally, I understand that there is a margin added to this distance. However, if a pilot unintentionally flares too long, or an updraft occurs, how does the pilot know when there is no longer enough runway to land (and must execute a go around)? Does the landing-distance-margin necessarily account for these long landings?

P.s. This is my first airliners.net post, so I hope this is the correct forum! :)

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 1:28 pm
by chimborazo
In the vast majority of cases for commercial flying they fly into runways with marked touchdown zones. Look at runway markings on Wikipedia. If you haven’t touched down in the touch down zone you go around/abort the landing (assuming spoilers not up).

GA into fields etc you should kind of “know” if you are long.


There is a famous video in many compilations on YouTube of a twin crash into the sand at the end of St Bart’s runway due to floating half way down the runways before touching down and not having enough distance to stop. Getthere-itis. To be fair I don’t know the background- maybe they were low on gas and had to make the landing....

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 1:45 pm
by GalaxyFlyer
Runway markings plus many runways have distance remaining signboards off the side, especially military ones—very useful. No extra distance for improper technique, the calculations are based on “flare distance” touchdown and braking. Most air carrier runways are generously long for landings as take-off distance drives runway design.

Flare distance is from 50’ (16m) over the beginning of the landing surface to touchdown; typically assumes retarding the throttles to idle at about 40’ and ranges between 1500’ and 1900’. The “actual landing distance” (flare plus braking) must be multiplied by 1.67 to becomes the minimum runway length. Plus any adjustments for wet or contamination.

GF

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 2:04 pm
by BravoOne
Some operators have installed this system: Honeywell RAAS, Runway awareness and advisory system. You are more likely to see it in high end corporate aircraft but there are a few airlines that have spec'd it in new deliveries as well.

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 2:28 pm
by GalaxyFlyer
Yes, it’s in the Globals and 650. I believe it’s in the EGPWS, just add the performance database specific to landing, any standards on touchdown and pin the system to display, IOW, not very expensive as aviation goes—maybe $40,000 per.

EK has it on their B777 fleet because that’s how the landing-go around accident started. RAAS said “long landing”; pilot started to go around as dictated by SOP; plane touched down, auto throttles were disengaged as it was on the ground; pilot selected TOGA, system said, “no you’re not, you’ve landed”.

GF

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 2:48 pm
by CosmicCruiser
where I was if you landed "long" and yet still made it you would be debriefed for poor judgement. A G/A lets you start from scratch as opposed to trying to salvage it.

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 4:44 pm
by Woodreau
In order to dispatch to a destination airport, the required landing distance needs to be within 60% of the available landing distance.

So even though I can get an aircraft (say an A320) stopped within 4000ft, if an airport only has a 4500ft runway, the flight cannot be dispatched to that airport. if the required landing distance for an aircraft is 4000ft, then the minimum runway length required for the airport is 6700ft. (6,666ft) in order to dispatch to that airport.

Once the aircraft is dispatched and in the air, then the minimum runway length required to land at any airport is required landing distance plus 15%, so in the example, if the required landing distance is 4,000ft, then the minimum length runway is 4,600ft.

FAR 121.195b
https://www.ecfr.gov/cgi-bin/text-idx?S ... 5&rgn=div8

Re: Landing Distance/Go Around Question

Posted: Wed Aug 28, 2019 10:19 pm
by AndrewJM70
Many airlines use the touchdown zone markers. BA for example make a GA mandatory if the aircraft has not touched down by the last marker. This can be quite harsh at an airport like LHR where 9,000ft plus is available after that last marker. A short-haul aircraft can be stopped comfortably within half of that distance but they have to go around none the less. If a pilot lands long, he or she gets a note from management. Too many times and it is tea and biscuits with the chief pilot.

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 5:49 am
by themathguy
Thanks all for the responses! I really appreciate it!

Pilots using runway markings and RAAS make sense to me.

I just have a question about a rare/special case in a plane without RAAS:

-Suppose the "in-air" landing distance is greater than the dispatched distance (due to runway contamination). And the distance calculated is 8000' = 6800' + 15% margin (1200')

-Suppose the flare distance is normally 1500'.

-If landing on an 8000' runway, there would be touchdown zone markings 3000' from the threshold. If a pilot unintentionally didn't touch down until the end of these markings, the pilot's flare distance would be 1500' too long. ...But the 15% margin only covered 1200'.

In such a case, would pilots brief accordingly? Sorry if this is confusing!

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 11:32 am
by CosmicCruiser
not following your math BUT where I was the computed ldg dist included the 1500' over fly to the touchdown point so if the computed dist was 7,000' you would touchdown 1500' from the end and need 5500' to stop. We used quick reference tables until the weather went down to to a given level then we had to use the PAT (Performance computer) for a more accurate dist. I never saw any issues as a rule but a few times landing on ungrooved runways when it was raining did create problems. CDG, DEL & BOM come to mind.

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 1:59 pm
by GalaxyFlyer
themathguy wrote:
Thanks all for the responses! I really appreciate it!

Pilots using runway markings and RAAS make sense to me.

I just have a question about a rare/special case in a plane without RAAS:

-Suppose the "in-air" landing distance is greater than the dispatched distance (due to runway contamination). And the distance calculated is 8000' = 6800' + 15% margin (1200')

-Suppose the flare distance is normally 1500'.

-If landing on an 8000' runway, there would be touchdown zone markings 3000' from the threshold. If a pilot unintentionally didn't touch down until the end of these markings, the pilot's flare distance would be 1500' too long. ...But the 15% margin only covered 1200'.

In such a case, would pilots brief accordingly? Sorry if this is confusing!


The vast majority of planes don’t have RAAS, it’s relatively new (10 years or so) and most airlines didn’t spec it. As was said elsewhere, it is a skill-based profession meaning the data has to be translated into action by the flying pilot and a rather quick decision made if it isn’t happening. That’s why the briefing, it establishes the decision beforehand, “if we’re not down by here, we’re going around. It’s a case of “bringing your A Game when the runway available and required are closing together.

In the bizjets I flew, we briefed, used the HUD and the flying pilot called out touchdown point as shown by the flight path vector. If a short-ish runway (LDR inside of the factored distance), it was briefed, speed was within 5 knots of Vref, no tailwind, autobrakes LOW or MED. In a Global, that’d likely be runways shorter than 5,000’. I e landed the C-5, sans any aids on 6,000’ and done hundreds of touch and goes on 7,000’

GF

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 2:32 pm
by vikkyvik
CosmicCruiser wrote:
not following your math


What he's saying is that the margin for error (15%, or 1200 feet in his example), did not cover the actual error (18.8%, or 1500 feet, in his example).

Essentially, if we use a 1500' flare distance, then some percentage of flights will touch down past the 1500'. I've been on plenty that have touched down around 2000' down the runway.

I think maybe what's needed is the assumptions that go into the landing distance calculation. Like, what brake setting is used in the calcs?

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 3:01 pm
by GalaxyFlyer
The certification standard used to create the charted distances assumes maximum anti-skid braking using brakes worn to the minimum spec, so pilots aren’t going to reduce the stopping distance by a great deal. Using autobrakes, the specified deceleration rate of the setting—LOW, MED, HIGH. Only RTO uses maximum braking.

GF

Re: Landing Distance/Go Around Question

Posted: Thu Aug 29, 2019 4:15 pm
by BravoOne
Taking this one step further, Airbus has certified a new Brake to Vacate mode on some of there fleets.

https://en.wikipedia.org/wiki/Brake_to_Vacate

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 2:24 am
by BoeingGuy
BravoOne wrote:
Taking this one step further, Airbus has certified a new Brake to Vacate mode on some of there fleets.

https://en.wikipedia.org/wiki/Brake_to_Vacate


Boeing will have something similar on the 777-9. Called Brake to Exit.

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 4:11 pm
by LH707330
BoeingGuy wrote:
BravoOne wrote:
Taking this one step further, Airbus has certified a new Brake to Vacate mode on some of there fleets.

https://en.wikipedia.org/wiki/Brake_to_Vacate


Boeing will have something similar on the 777-9. Called Brake to Exit.

Someone in Marketing must have said "Whatever you do, don't use the same wording that the other guys do for the same thing." Meanwhile, pilots have to learn duplicate vocabulary. One would think that OEMs would have a terminology standardization body to avoid this.

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 5:50 pm
by GalaxyFlyer
Trademarks!

GF

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 9:38 pm
by zeke
BravoOne wrote:
Some operators have installed this system: Honeywell RAAS, Runway awareness and advisory system. You are more likely to see it in high end corporate aircraft but there are a few airlines that have spec'd it in new deliveries as well.


That dumb system that told the EK 777 crew to go around with 3100 m of runway in front of them. It only looked at the 1000 m behind them not the 3100 m in front.

BravoOne wrote:
Taking this one step further, Airbus has certified a new Brake to Vacate mode on some of there fleets.

https://en.wikipedia.org/wiki/Brake_to_Vacate


ROW/ROPS is available on all Airbus types, some it standard, some it’s optional.

BoeingGuy wrote:
Boeing will have something similar on the 777-9. Called Brake to Exit.


I don’t think it is that similar, Airbus has the patent on it and Boeing refuses to licence it.

BTV is a byproduct of ROW/ROPS, it’s main purpose is not minimum runway occupation (the aim of BTV). It is dynamic runway overrun protection whilst airborne and after touchdown.

It looks at the aircraft weight,speed,cg, configuration and environmental conditions whilst airborne and tells them to go around if required. Once on the runway it looks at the actual braking performance and runway available and then modified the braking schedule or tells the pilots to apply maximum braking.

It works on dry, wet, and contaminated runways.

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 10:02 pm
by GalaxyFlyer
It wasn’t the dumb system, it did its job by the aural warning “Long Landing”. The dumb system was an SOP that took judgement away from the pilots who clearly could the 3100m remaining.

GF

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 10:02 pm
by GalaxyFlyer
It wasn’t the dumb system, it did its job by the aural warning “Long Landing”. The dumb system was an SOP that took judgement away from the pilots who clearly could see the 3100m remaining.

GF

Re: Landing Distance/Go Around Question

Posted: Wed Sep 04, 2019 11:29 pm
by BoeingGuy
zeke wrote:
BravoOne wrote:
Some operators have installed this system: Honeywell RAAS, Runway awareness and advisory system. You are more likely to see it in high end corporate aircraft but there are a few airlines that have spec'd it in new deliveries as well.


That dumb system that told the EK 777 crew to go around with 3100 m of runway in front of them. It only looked at the 1000 m behind them not the 3100 m in front.

BravoOne wrote:
Taking this one step further, Airbus has certified a new Brake to Vacate mode on some of there fleets.

https://en.wikipedia.org/wiki/Brake_to_Vacate


ROW/ROPS is available on all Airbus types, some it standard, some it’s optional.

BoeingGuy wrote:
Boeing will have something similar on the 777-9. Called Brake to Exit.


I don’t think it is that similar, Airbus has the patent on it and Boeing refuses to licence it.

BTV is a byproduct of ROW/ROPS, it’s main purpose is not minimum runway occupation (the aim of BTV). It is dynamic runway overrun protection whilst airborne and after touchdown.

It looks at the aircraft weight,speed,cg, configuration and environmental conditions whilst airborne and tells them to go around if required. Once on the runway it looks at the actual braking performance and runway available and then modified the braking schedule or tells the pilots to apply maximum braking.

It works on dry, wet, and contaminated runways.


The 777-9 has a system that does that too. It’s called ORW or Overrun Warning. That’s not what BTE does.

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 1:46 am
by zeke
BoeingGuy wrote:
The 777-9 has a system that does that too. It’s called ORW or Overrun Warning. That’s not what BTE does.


Is that part of RAAS ? what I have read about RAAS it is a dumb system built into the EGPWS, does not dynamically look at conditions, aircraft, or actual braking performance.

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 1:59 am
by BoeingGuy
zeke wrote:
BoeingGuy wrote:
The 777-9 has a system that does that too. It’s called ORW or Overrun Warning. That’s not what BTE does.


Is that part of RAAS ? what I have read about RAAS it is a dumb system built into the EGPWS, does not dynamically look at conditions, aircraft, or actual braking performance.


No it’s not part of RAAS. RAAS is not available on the 787 or 777X due to system architecture and the fact those airplanes have stuff like Airport Moving Map displays.

ORW is a 2019 technology system not a slap on system like RAAS. Yes it uses dynamic performance.

Honeywell does all these slap on EGPWS additions that are often a solution looking for a problem. I’m kind of in your camp on this.

If it calculated stopping distance is in doubt it will give alerts in air or after landing. It’s all dynamic performance and can be inhibited, such as for a Flaps 20 landing.

On the ground it gives a Time Critical Warning “MAX BRAKES, MAX REVERSE”. In the air it says something “GO AROUND”. I forget the complete alert.

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 2:00 am
by zeke
Interesting, looking forward to reading more on it and how they bypassed the patent.

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 2:07 am
by BoeingGuy
zeke wrote:
Interesting, looking forward to reading more on it and how they bypassed the patent.


The 777-9 has a lot of cool new features. Another example is providing some Autopilot capability when in the Secondary Flight Control Mode, such as due to loss of air data. Also has a detected AIRSPEED UNRELIABLE Warning alert. (The 787 has this as an Advisory message and also has backup synthetic AOA Speed and GPS Altitude in the event of Air Data issues.)

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 3:45 am
by zeke
BoeingGuy wrote:
zeke wrote:
Interesting, looking forward to reading more on it and how they bypassed the patent.


The 777-9 has a lot of cool new features. Another example is providing some Autopilot capability when in the Secondary Flight Control Mode, such as due to loss of air data. Also has a detected AIRSPEED UNRELIABLE Warning alert. (The 787 has this as an Advisory message and also has backup synthetic AOA Speed and GPS Altitude in the event of Air Data issues.)


In the A350 with a loss of all aircraft air data, they just use the engine air data computers.

Re: Landing Distance/Go Around Question

Posted: Thu Sep 05, 2019 8:06 pm
by BravoOne
As I have understood this AP availability in the secondary mode, is its a min requirement for removing the pilots from the flight deck. Now don't get all twisted around the axle, but it is a well known fact that Boeing is working on this concept with a target date of 2025+.

Re: Landing Distance/Go Around Question

Posted: Fri Sep 06, 2019 2:46 am
by BoeingGuy
BravoOne wrote:
As I have understood this AP availability in the secondary mode, is its a min requirement for removing the pilots from the flight deck. Now don't get all twisted around the axle, but it is a well known fact that Boeing is working on this concept with a target date of 2025+.


Not even close for passenger jets. The NMA isn’t even looking at a one person flight deck, let alone zero pilots.

AP availability in Secondary Mode is intended as a pilot workload reduction if there is an air data or other issue that puts you in a secondary mode. Nothing more to read into it.

Re: Landing Distance/Go Around Question

Posted: Fri Sep 06, 2019 1:17 pm
by BravoOne
No one said anything about passenger jets, although if it works in a freighter, it should work on any similar model airframe.

I disagree regarding the underlying intent, as the availability of the AP in secondary mode is significant as Boeing moves forward on a single pilot/no pilot future aircraft according to the Flight Control folks. I don't agree with the concept but then they don't ask my opinion. The pilotless/single pilot aircraft is a future fact of life until the first accident

Re: Landing Distance/Go Around Question

Posted: Mon Sep 09, 2019 6:43 am
by Passedv1
themathguy wrote:
Thanks all for the responses! I really appreciate it!

Pilots using runway markings and RAAS make sense to me.

I just have a question about a rare/special case in a plane without RAAS:

-Suppose the "in-air" landing distance is greater than the dispatched distance (due to runway contamination). And the distance calculated is 8000' = 6800' + 15% margin (1200')

-Suppose the flare distance is normally 1500'.

-If landing on an 8000' runway, there would be touchdown zone markings 3000' from the threshold. If a pilot unintentionally didn't touch down until the end of these markings, the pilot's flare distance would be 1500' too long. ...But the 15% margin only covered 1200'.

In such a case, would pilots brief accordingly? Sorry if this is confusing!


First off, when you calculate a landing distance you are counting the air run so if you calculated 6,800 feet, it really means you have an air run of 1,000 feet, and then a ground run of 5,800 feet. Also know that credit is not taken for reverse thrust so in most situations that gives you plenty of added buffer.

If you get to a runway, and it is unexpectedly contaminated with snow and you don't have the numbers to land...you don't land. You are going somewhere else.

Most of the time, you are landing on a runway that is plenty adequate. In that case, as long as you put it down in the first 3,000 feet of runway, you are plenty fine. If you aren't going to make it in the first 3,000 feet then a large commercial aircraft is required to go around. Does that happen every time? No, but you are really sticking your neck out by continuing the approach. The touchdown zone is over 1/2 of a mile long, if you can't touchdown within that then things are screwed up to the point where you should not be attempting a landing.

For short runways, a Latest Touchdown Point is calculated. If you are landing on a 6000-foot strip and calculate that your landing distance is calculated at 5,000 feet then you subtract your air run which gives you your 4,000 foot gound run. Subtract your ground run from your Landing Distance Available and you get 2,000 feet. 2,000 feet is two tick marks past the fixed distance markers. If you aren't on the ground by then, you go around.