View Full Version : Touchdown point

5th Jun 2023, 16:48
Hello guys
FAA SAFO19001 of 3/11/19 in para g TOUCHDOWN POINT gives air distance as 1500ft or 07 secs to touchdown. It also states that operators can use shorter distance of 1000ft or 04 secs to touchdown provided some requirements given there are fulfilled.
I have seen all Airbus operators using 7 secs to touchdown. Are there any Boeing 737 carriers who use 4 secs or 1000ft to touchdown? If so Are they giving required training?

12th Jun 2023, 06:45
Since no one is answering the full question can some pilots of B737 carriers atleast tell me if their landing distance consists of 1000ft threshold to touchdown air distance?

Luc Lion
12th Jun 2023, 07:49
(removed a stupid statement)

12th Jun 2023, 10:13
Unable to address the specifics of the question, but the FAA text appears to equate to similar EASA text. (CAT.POL.A.350 Approval of short landing operations).
However there are significant differences in that EASA applications are requirements whereas FAA is advisory; also that EASA applications (past experience) relate more to turboprop than jet operations.
Furthermore, anecdotal evidence (significantly from this forum) is the the 737 is not the best aircraft type to consider for such a dispensation based on accident / incident records.

Practical considerations might consider dispensation for a reduced TCH (not EASA), and if so what are the obstacle clearance implications.
Or a duck-under manoeuvre, a different flare technique than that recommended by the manufacturer, or safety margins in landing distance.

The ICAO Performance Manual Appendixes cover a wide range of issues, which as above suggest that an alternative operation should considered very carefully:

Re question #1, considered in Appx 4 (~page 48)


n.b. Appendix 7. Pilot Procedures and Flying Techniques when landing on length limited runways.

Appendix 9. Policy on Landing Distance Margin.

Appendix 12. Requirements for Operator and Pilot Training

Re question #2, the normal published performance is more likely to be based on AC 25-32 para 8.2 which suggest air distances greater than 1000ft


n.b. judgmental text: 8.1.3
- consistently executed in service by crews of average skill;
- methods or devices that are safe and reliable;
- allowance for any time delays that may reasonably be expected in service.

12th Jun 2023, 12:33
I'm a little confused as, for the narrow bodies (which is my background)

(a) a 1000 ft visual aiming point for a 3 deg slope brings the wheel height well under 50 ft coming over the keys. Not at all sure that I like the idea of bringing the aiming point back to achieve an earlier touchdown point ?

(b) since the 737 has been noted, I always found it to be a pussy cat to land - drive it down to the aiming point on speed, a touch of flare and paint it onto the runway. Worked pretty well near all the time. Touchdown point probably 1300-1500 ft typically.

(c) the normal distance factor gives adequate fat for the great majority of landings. If things are tight, then the touchdown can be a tad more pointed and brake and reverse use more aggressive. If things are too tight, I think I would prefer to go elsewhere rather than duck under indiscriminately (uness the obstacle profile is totally benign).

Or am I just getting way past it ?

PS. Perhaps 70 Mustang might consider reinstating the deleted posts - I thought both to be useful and pertinent to the discussion.

12th Jun 2023, 14:00
Boeing was mentioned because all A320 carriers documents take air distance as 1500ft or 7sec to touchdown from threshold. But I found one Boeing carrier out of the three that I know were operating using 1000ft air distance while other two used 450mtrs or 1500ft. As mentioned in the SAFO 19001 to use 1000ft air distance pilots need to be trained to recognise 1000ft point, touch down and if unable then to go around. There are other conditions like RW marking of 1000ft. etc. My question is are these conditions mandatory or advisory. Because the carrier that's using 1000ft air distance had overrun problems including two fatals due to long landings. Offcourse it wasn't due to only 500ft but by a long way. But can carrier use 1000ft or four secs to touch down without fulfilling necessary requirements?

12th Jun 2023, 14:49

a) I agree, but the FAA appears to allow this, EASA not so.
If the FAA requires 50ft TCH then this implies a steeper approach; what approach guidance is required, stabilised approach, etc.

b) I defer to the expertise. However considering the overall stopping distance, is the reduced air distance taken as a performance improvement. Is this justified by the basis of and assumptions in the published landing performance; I fear not.

c) what distance factor is considered; adequate and majority suggest that all contributing data will be available and accurate, and well judged.

12th Jun 2023, 14:57
vilas, … are these conditions mandatory or advisory …

This depends on whether the operator is operating under EASA or FAA approval.

EASA (or equivalent) is a requirement - prior approval - the operator shall provide evidence - CAT.POL.A.350

FAA is advisory - the Operational Landing Distance data used is advisory data based on the recommendations of AC 25-32 - The guidance in this AC is neither mandatory nor regulatory in nature and does not constitute a requirement. … to provide guidance to manufacturers for a standardized approach for computing time-of-arrival landing performance data - (which it appears not to do so for FAA operations).

I do not recall that Airbus publishes data for anything other than EASA FOLD performance. Thus FAA Airbus operators would be expected to use this, excepting dispensation (SAFO19001) where alternative, advisory data, would be based on AC 25-32.

13th Jun 2023, 10:28
Some technicalities :
When aiming the pilot eye (or ILS antenna) on a 3° slope to the 300m marker, the gear will go over the threshold at a significantly lower height.
For a medium size jet, you're about 4.5m high, to which you add a 3 to 5° pitch angle times 15.5m, that's about one more meter.
So your gear will be above threshold at around 9.5m and would impact the runway at about 190-200m if you did nothing.

However, any flare even a very late (but successful one) will bring you well over the 300m mark. Usually a very good landing is done at 400m. Anything before that can usually be hard (assuming a correct height over the threshold obviously).

So I don't understand how any operator could guarantee 300m landings everytime.
Maybe they plan to approach lower : "Approach guidance is consistent with a shorter air distance"
Which wouldn't shock me as long as there was a sufficiently long displaced THR or similar clear area before it. But it isn't allowed at my operator, we land between 1000 and 2000ft (some similar operators will allow up to 3000ft)

However, at least for airbus aircraft, I noticed the flysmart perf app is very pessimistic when it comes to landing distance.

13th Jun 2023, 11:07
Some of these threads do get rather interesting ...

A320 carriers documents take air distance as 1500ft or 7sec to touchdown from threshold

Right or wrong, my line observations are that 1500 ft (or a tad less) is a pretty typical "good" distance to touch. My main concern with trying to make the geometry too simple is that we start to neglect the realities of the landing flare. If the aiming point is whatever, then the touchdown has to be further in unless we are talking tailhook operations. The skilled operator can flare the aircraft on with minimal distance lost- most of us can only aspire to that level of judgement except on the occasional landing where it all comes together, usually quite independent of pilot finesse.

The two main hazards with which we must contend are landing in the dirt (I've only done that once as a relative newchum on a light aircraft - my introduction to night ops when a good fog rolls in unexpectedly) or really mishandling the flare and floating and floating where the discipline to call the miss is critical (lots of time on the 722 tended to cure that float problem fairly quickly). Unless the pilot is faced with minimal distance pad, for whatever reason, I see little point in exposing the operation to these hazards as a routine protocol.

but the FAA appears to allow this, EASA not so.

I suspect that I prefer EASA's thinking.

If the FAA requires 50ft TCH then this implies a steeper approach; what approach guidance is required, stabilised approach, etc.

Indeed. If an assumption can be made that tight runways generally are going to be shorter and less well equipped facilities, this just flies in the face of all the wisdom inherent in repetitive stabilised approaches ?

is the reduced air distance taken as a performance improvement.

This is another nail in the coffin. Providing that we can address the float/miss consideration satisfactorily, we are juggling nickels and dimes while walking blindfolded through quicksand grounds. Why expose the operation to a variable increased risk scenario for scant reward in the overall scheme of things ?

all contributing data will be available and accurate, and well judged.

Except on those occasions when it's not ....

As always, the aim is to hit the runway and nothing else.

13th Jun 2023, 17:35
I can't assist much with academic part of the question. I am quite sure our performance calcs assume 455 m flare (increased from 305 m years ago). It's probably written in the ReadMe for our third party performance app.

These days I am not so interested in what the book says anymore. The reality involves glide slopes of varying quality, glide slope PAPI mismatches, non-standard runway markings, short- and slippery runways. The PAPI and G/S enhances the visual references for judging your path and obstacle clearance. When visual references can be establised in other ways it's an eyeballing exercise. No need to land longer than necessary. All in my opinion, of course.

13th Jun 2023, 18:53
also FYI that at many airports, PAPI is not perfectly aligned with G/S path.

Doors to Automatic
21st Jun 2023, 23:44
Out of interest how is the threshold crossing height determined?

At a standard descent rate and 150 mph landing speed an airliner would cross the threshold at 53ft to get to zero by 1000ft in. Allowing for the flare would take this to around 1500ft which I seem to remember is the reason why airports moved the aiming point marker some years back.

23rd Jun 2023, 05:36
My question remains if an airline doesn't impart the required training for 4secs/1000ft to touchdown but their performance is calculated on that, if an overrun occurs will it be blamed for faulty performance parameters?

23rd Jun 2023, 14:03
An interesting question: "how is the threshold crossing height determined? "

Several documents refer to, or infer wheel height as the basis of landing performance:

AC 91-79 para 6. g. Excessive Height Over the Runway Threshold – Threshold Crossing Height (TCH) Greater Than 50 ft (Excess TCH).
The certified landing distances furnished in the AFM are based on the landing gear being at a height of 50 ft over the runway threshold. For every 10 ft above the standard 50 ft threshold height, landing air distance will increase 200 ft. ( but the wheels will be much lower when following visual guidance; - see Min Eye Height below and # 9).

ICAO performance Manual
Air Distance. The length of the airborne distance from a point above the threshold to the point of main gear touchdown should be representative of a distance achievable in line operations following normal procedures and in line with the approach guidance provided.
(This suggest TCH referenced to wheel height.)

Airport information for visual guidance e.g. PAPI, publish a Min Eye height over the threshold. Note some runways have a second set of long body PAPI, suggesting that the increase is related to wheel referenced TCH.

References to PANS OPS / ICAO OPS (not verified) define a Reference Datum Height as The height of the extended glide path or a nominal vertical path at the runway threshold.
According to ICAO Annex 10, the height of the ILS reference datum for ILS will be 15 m (50 ft). A tolerance of plus 3 m (10 ft) is permitted.

FAA Aeronautical Information Manual (unverified) defines Threshold Crossing Height : The theoretical height above the runway threshold at which the aircraft’s glide slope antenna would be if the aircraft maintained the trajectory established by the mean ILS glide path.

The GS is increasingly irrelevant at lower altitudes due to angular sensitivity, parabolic effect, … Thence discussions on height difference; eye - ILS antenna - wheel, which are aircraft type dependent.
ILS GS is unlikely to agree with visual guidance with decreasing altitude.

Note, pilots more often refer to a fixed position for touchdown point, ground distance.
Performance calculations are based on air distance ( with corrections ) which gives a spread of touchdown position.

Also see, Theory, - (note ref to Reference Datum Height and assumptions) page 11, para 331
Reality, - page 30, fig 16; page 31, fig 17, et al, "The influence of the threshold crossing height appears to have the strongest influence on the airborne distance."

Re previous discussion defining touchdown:-
AC 91-97 Appx 1, para 2 I … the TDZ is referred to as a point 500-3,000 ft beyond the runway threshold not to exceed the first one-third of the runway.
This reference is not used in landing distance performance calculations.

23rd Jun 2023, 16:16
My question remains if an airline doesn't impart the required training for 4secs/1000ft to touchdown but their performance is calculated on that, if an overrun occurs will it be blamed for faulty performance parameters?

Not sure if this is what you refer to...

We use 1000ft flare distance for dispatch calculations. Story is it allows for a slight increase in dispatcheable max payload in certain conditions (as I understood better ACMI capability on certain destinations?). The enroute (advisory) calculations keep1500ft flare distance. Back in the day when the change was made, instructors were made aware, but no specific training was done as we had procedures that required to recheck landing performance enroute (1500ft flare).

23rd Jun 2023, 17:53
vilas: "if an airline doesn't impart the required training for 4secs/1000ft to touchdown but their performance is calculated on that, if an overrun occurs will it be blamed for faulty performance parameters?"

We should not infer blame - a judgement after the event.
Instead consider beforehand; if the regulator has given permission to use 1000ft, then who checks its use and the achieved landing performance; safety margin - SMS, Flight Data Monitoring.

Of course if the regulator accepts the advisory interpretation, placing responsibility on the operator, then the risk of overruns could be higher,… but who would know.

A safety weakness in advisory 'regulation' and monitoring of that.

BB, but even for dispatch the critical parameter is the overall landing distance.
Whilst some authorities still allow operators to use generic data before flight (1000ft), all operators (either by requirement of advice) are required to check that the landing will be safe based the Factored Operational Landing Distances (≈1500ft) - as apparently you do.

However, if pilots invoke 1000ft flare before landing, is this by regulation or advice; and in either case this should be trained-for, checked, etc, as per vilas.