Displaced Thresholds.

[ac500u]

If a runway has a permanently displaced threshold due only to obtacles on the approach, can a pilot legally touch down prior to the displaced threshold if he has safely cleared the obstacles?

If someone knows exactly where the law allowing/prohibiting this is located, that would be of great assistance.

I've found the regulation in the Canadian AIP, but am unable to locate it in any other legal document, JAR or otherwise.

Thanks for your help.

[OzExpat]

So far as I'm aware, the area prior to a displaced THR need not be maintained to the same structural integrity as the area beyond the displaced THR. In this country, the area prior to the displaced THR can be used to line up for take-off, but definitely not for landing.

In any event, you may not be aware of the location of the obstacle that has created the need to displace the THR. Thus it would seem to be most unwise to try to land prior to the THR, as this may entail the use of a different approach path that might conflict with the controlling obstacle. Better to refer to the displaced THR and, therefore, be sure that you and your pax will be safe.

[alexban]

How would you know you've safely cleared the obstacle? Gear still attached?
Why would you want to land before the threshold? Want to prove something?...Anyway you paid for all the rwy,you get no discount for using only half of it...:ok:
Brgds....

[Old Smokey]

To repeat the question of alexban, and a thousand others who didn't ask the question.....

Why would you want to land before the threshold?

Old Smokey

[Scando]

Because the runway is contaminated with snow, slush or ice, and 2000 meters is a lot better than 1800, even if you can legally land on 1800m?
Not all of us operate on 3000m+ runways the whole time.

[john_tullamarine]

The days of "winging it" have long gone.

Now the catchcry is, or should be, risk assessment, control, and mitigation/minimisation.

(a) There is a risk in landing past a displaced threshold - no argument.

(b) There is a good likelihood that this risk will increase significantly if the runway is contaminated.

(c) Unless fuel is the driving critical factor, the mitigator is to divert, perhaps ?

If one "ducks under", one

(a) loses the benefit of visual or electronic slope guidance

(b) one assumes a higher risk of a heavy landing and/or tailstrike

and so the argument can go on ...


In the first instance, you pays your money and takes your chances ..

and, in the second ... which of the various scenarios would you prefer to have to defend in court after the accident .... ?

[ac500u]

Well, thanks for all the opinons, but noone really answered the question.

The most common reason to displace a threshold is because of obstacles on the approach. If that obstacle is behind you, can you legally touch down on the perfectly maintained, load bearing surface prior to the threshold? If not, where is this LAW stated? If so, where is this law stated?

There are a million reason t want to touch down before a displaced threshold. If a runway is 2500ft long, with a 600ft displaced threshold, and your aircraft requires 1899 ft to stop, that 600 is invaluable.

Many obstacles which are the cause for displaced threshold are off the centerline of the runway, but withing the 5degree cone of approach. As a pilot, it is easy to tell once you've past an obstacle, without bouncing the gear off of it.

Opinions are great, but facts, and quotes are better.

[john_tullamarine]

I guess it is a case of the law being what the judge delivers in his decision. However, if the start of the LDA is here, and you land before that, does that not suggest that you might be landing other than on the runway ? Whether the surface is seal or not might not be held to be all that important if things go awry ...

Seeing you are in a lovely area ... I think I can guess which hills you are coming over landing toward the sea ... quite a displaced threshold, indeed ... I have some pix tucked away somewhere at home of Otters and Nomads probably 30-40 ft above the cars a long way from the runway ........

[ac500u]

Out of interest to everyone with a negative opinion, the law in Canada (ICAO) can be found at the following link....

http://web.elastic.org/~fche/aip/AIP-01-05-95.html

It clearly states that you CAN land on the surface before the threshold, at least in Canada.

I am very interested in locating any other regulation, JAA, FAA, or otherwise that clearly states a position, negative or positive, as I can't find any.

Any help would be greatly appreciated.

[john_tullamarine]

(a) in many places, AIP is not law but rather an interpretation by the regulator couched in terms of operational expectation ?

(b) probably it would be sensible not to crash prior to the point at which the particular aircraft had the benefit of ICAO (or local, if more restrictive) approach gradient obstacle clear requirements met ?

At day's end, the pilot has the immediate capability of doing whatever he chooses whether his peers view such as being either sensible or not.

However, it is the judge who determines the penalty, if any, following the enquiry consequent to the accident ...

[BOAC]

I-Ford - I think there were other issues in at least one of the GOA 'incidents' and in view of the amount of metal 'under your feet' on finals there I would be very reluctant to 'land short' on that runway!

IMO if you cannot guarantee stopping in the available runway length - do something else - dire emergencies excluded, of course. The reference you link to clearly says it is the pilot's responsibilty to maintain safety - which is ALWAYS the case, and I can see NO reason to land 'short' in normal ops. I would suggest that the question 'is it legal' is less relevant than 'is it sensible'?

If, OTH, your aircraft can fly, say, a 5 or 6 degree slope, then perhaps you can apply for an alleviation, but equally the types that can do that should not need more than 2100mtrs?

As to whether it is 'legal', I would suggest that you would not encounter a problem from the airport authorities providing the surface is 'suitable', but as is the case of R29 at GOA your operating company may wish you to explain a significant 'below gp' event or a high rate of descent at a late stage - or even worse, a piece of dockyard crane in your undercarriage.:D

[safetypee]

A steep approach (5-6 deg) should qualify for a reduced threshold crossing height (35 ft), which in turn gives an increased LDA from the geometry.
Duck under – well don’t try that from the ‘city end’ at London City Airport as the bridge and road lights get very close even with a 1:29 OFS.
How do you ever know that you have missed all of the obstacles? A typical human assumption that often precedes errors and accidents; don’t duck under / land before the threshold.

[westhawk]

The original question had to do with finding specific rules governing the allowed uses of displaced threshold runway surface in various countries, If I understood the question correctly. In the USA, I am unaware of any specific regulation on this subject. However, the AIM guidance on runways and their markings indicate that the runway area prior to the threshold markings (displaced threshold marked by arrows) is not available for landing touchdown, even though it is available for takeoff, taxi and rollout. FAA actions against pilots sometimes cite the pilot's disregard of the AIM guidance on an issue as evidence of a FAR 91.13 "Careless or wreckless" violation even though the FAA officially refer to the AIM as "non-regulatory guidance" or "advisory in nature". In other words, you may not be legally required to follow this "advise", but if something goes wrong....

Runway thresholds may be displaced for any of a variety of reasons other than obstacle clearance plane considerations. These include, but are not limited to, ILS navigation signal integrety requirements, pavement structural strength requirements or even airport neighbor concerns about low flying aircraft and noise. One southern California municipal airport with a stong anti-airport contigient proposed displacing the runway threshold to discourage it's use by jet operators. So far, FAA does not support this course of action.

Under FAA regulations, large and turbine powered aircraft must maintain at or above any electronic or visual glidepath guidance while approaching the runway and may not descend below this path until necessary for safe landing. Vertical guidance is typically aligned so as to provide for a threshold crossing hieght of 50'. Glideslope angle may be raised above the standard 3 deg. and/or the threshold may be displaced to provide required obstacle clearance. On shorter runways, contaminated runways or with adverse wind components, It may sometimes require that vertical flight path angle and aim points be adjusted in order to intersect the runway surface at an acceptable rate of closure at the required touch down point for the situation. These adjustments must still allow conformity with applicable stabilized approach requirements and safe obstacle clearance. Under these conditions, firm touchdowns and maximum allowable braking may be required. Aiming shorter to land sooner or touch down softer IS commonly done by many pilots but it must be understood that there is little defense if something goes wrong. In low visibility conditions or at unfamiliar fields, especially at night, many accidents have been traced to pilots succumbing to visual illusion and hitting obstacles. Intentionally landing short of the threshold marking is not normally viewed as acceptable except in the most extraordinary circumstances of emergency. Normal approach profiles intersect the runway surface at aproximately 700-1000' beyond the threshold marking depending on the specific descent angle. Roundout places the touchdown point somewhere beyond this. The higher above and further forward the pilot sits relative to the main wheels at threshold crossing attitude, the closer to the threshold the mains will touch and the closer the aircraft will pass to any ground obstacle in the flight path.

I realize that the above is not all clear, black letter law, but I hope it is helpful anyway.

Best regards,

Westhawk

[ac500u]

Let me be a little more specific.

A friend of mine was flying a light aircraft into a 2500 ft strip. This is a day VFR strip, with a permanently displaced threshold of 600 ft, due to obstacles on the approach. The dislacing obstacle is a 600 ft hill, ending 2 miles from the runway. It is very easy to turn final inside the hill, and avoid the obstacle all together, and is common practice at this airfield. The aircraft in question requires about 1800 ft to land at gross, and as this runway has 1900 available, it is perfectly 'legal'.

Long story short, the local authority was watching this particular day and witnessed him touching down before the threshold, and wishes to persecute him for it. Every single aircraft that day, and every day for the last 10 years has touched down before the threshold, but they chose him to penalize.

When he asked the authority where the regulation was located, he was informed that 'it is basic aviation knowledge'.

I personally don't feel that it is 'basic aviation knowledge' and wish to find the truth.

I would be perfect happy with either result. If it's illegal, I can give up my search, and admit defeat. If it's legal, he can point out the mistake to the authority.

Thanks in advance for everyone's help.

[metar]

If I remember correctly my PPL examiner told me that you can land on a displaced threshold so long as you aren't flying commercially. He actually pulled me up for NOT landing on it (it was runway 09 at Scone Airport, Perth).

I couldn't quote you the actual regulations though...

[westhawk]

ac500u,

Sorry I did not see the now obvious clues as to the situation you seek information on. I assume from the available clues that this took place in some Carib. Island nation or other. So only the specific rules in effect for the country of registry of the aircraft, the issuing country of the licence held by the pilot and the country where this occurred should be considered when researching the possible specific charges against your friend. If it was a national aviation authority who accuses the pilot of violating a rule, they should provide the specific charge in due course. If a local airport official, perhaps they just seek a "fine" be paid for the transgression. This has only happened to me in Mexico but I have heard of this practice elsewhere as well. If this is a CAA inspector or equivilant, I would advise your friend to consult with an aviation experienced lawyer/barrister before proceeding further.

I wish your friend the best in resolving the matter. Would like to hear how it plays out.

Best regards,

Westhawk

[mutt]

Ive seen a number of runways where the displaced threshold was protected with concrete blocks, landing short might turn out to be embarrassing. :)

Mutt

[ac500u]

The local authority down here has there own set of regulations that are loosely based on the older UK CAA regs. They are in a period of transition to new regs based on ICAO standards.

If they had simply said that my friend had broken rule 313.45 found on page 145 of the CARS, we all would've been happy and accepted the error.

However, they said that he broke the law, he said 'which law is that', they said 'it's basic aviation knowledge'. I found it highly insulting, as, if this is 'basic knowledge' then clearly I, and Transport Canada, have no basic knowledge.

I anyone knows where any regulations is located from ANY regulatory body that states that this is legal or illegal, I would greatly appreciate the assistance.

Thanks again.

[Spitoon]

I can't give you a definitive bit of law but I would offer the following (UK) orientated view.

A displaced landing threshold is the start of the runway for a landing aircraft.

It is quite conceivable that if the dimensions are suitable that there may be some other quite legitimate activity going on in the undershoot that the pilot would not be told about - even if the threshold was originally displaced because of an obstacle.

Although I would have expected ICAO to treat the situation in the same way the only reference that I can find in Annex 6 Part 1 is about precision approaches and says "An operator shall establish operational procedures designed to ensure that an aeroplane being used to conduct precision approaches crosses the threshold by a safe margin, with the aeroplane in the landing configuration and attitude."

[ac500u]

Regarding ' things going on, on the displaced portion that the pilot doesn't know about '... This would have to be covered in a notam. Any change to a runway, whether temporary displacement or otherwise, must be issued in a notam.

Also, if the area is unfit for surface movement of a/c it must be marked with X's or chevrons leading to the displaced threshold (not arrows).

[Ex Douglas Driver]

The Australian AIP has the following note associated with the diagram showing the undershoot area with a permanent displaced threshold:
"This section of runway available for all operations except landing in the direction indicated".
http://www.airservicesaustralia.com/publications/current/aip/ad/ad11120.pdf Go to Figure 5.

[ac500u]

Thanks ex-driver,

I wish however that they would be a little more explicit with the law. That looks like it is to be interpreted as being illegal to land before, but then they have the approach obstacled clearance slope end 60m before the displacement.

From a common sense point of view, I still can't understand why it would be illegal. You've cleared the obstacle, and the pavement is solid, at that point, what exactly is unsafe?

Thanks for the link. I guess that appears to be one for illegal.

Score now 1-1.

[OzExpat]

but then they have the approach obstacled clearance slope end 60m before the displacement.
You'll find that this is a design requirement from ICAO Annex 14.

[Ex Douglas Driver]

My question is "why"? What factors are coming in to play to require that extra runway before the displaced threshold?"

Airmanship (and the law) require that you know the landing distance required vs the landing distance actually available, before committing your tyres to the tarmac.

Landing distance available means the length of runway declared to be available and suitable for the ground run of an aeroplane landing.

For most operations, the Landing Distance Required calculated is factored to give "fat" to the demonstrated distances. This "fat" should be used to give a bit of breathing space during the landing roll, not an attempt to put the wheels just past the weeds.

For info, here are the factors for various aircraft weights here in Aussie (should be ICAO.....!)


...an aircraft must not land unless the landing distance available is equal to or greater than the distance required to bring the aeroplane to a complete stop,..., following an approach to land at a speed not less than 1.3 Vs maintained to within 50 ft of the landing surface. This distance is to be measured from the point where the aeroplane first reaches a height of 50 feet above the landing surface and must be multiplied by the following factors:

RPT SINGLE ENGINE AEROPLANES, CHARTER OPS, AERIAL WORK, & PRIVATE OPS
(a) 1.15 for aeroplanes with MTOW of 2000kg or less;
(b) 1.43 for aeroplanes with MTOW of 4500kg or greater;
(c) for aeroplanes with MTOW between 2000kg and 4500kg, a factor derived by linear interpolation between 1.15 and 1.43 according to the MTOW.

RPT MULTI-ENGINE NOT ABOVE 5700KG
(a) 1.15 for MTOW equal to or less than 2000kg
(b) 1.318 for MTOW equal to 3500kg
(c) for aeroplanes with MTOW greater than 2000kg but less than 3500kg, a factor derived by linear interpolation betwenn 1.15 and 1.318
(d)1.43 for MTOW exceeding 3500kg but not exceeding 5700kg

AEROPLANES ABOVE 5700KG - ALL OPERATIONS (Turbine and Piston)
for jet-engined aeroplanes
(a) 1.67 for RPT when landing on a dry runway, or charter on a wet or dry runway
(b) 1.92 for RPT landing on a wet runway (or the distance given in a wet runway landing chart

For propeller driven aeroplanes landing at a destination aerodrome
(a) 1.43 for a dry runway
(b) 1.67 for a wet runway

[Spitoon]

Regarding ' things going on, on the displaced portion that the pilot doesn't know about '... This would have to be covered in a notam. Any change to a runway, whether temporary displacement or otherwise, must be issued in a notam.

Also, if the area is unfit for surface movement of a/c it must be marked with X's or chevrons leading to the displaced threshold (not arrows).I'm afraid I'm going to have to disagree with you in part ac500u. If a displaced threshold is notified - either in the AIP or NOTAM - the pilot has been made aware of the area of runway that is available (in the example we're talking about, the area for landing). If all of the relevant obstacle clearance surfaces etc. are clear/sterile, there is nothing to stop an activity that doesn't compromise the OCS going on. Say the threshold is displaced by 500m, what's the problem with a vehicle crossing the normal threshold or someone digging a hole there. It's no different - from an OCS perspective - to the same things hppening outside the aerodrome boundary. That's why there are declared distances and OCS for every runway - it tells the pilot how much runway is available for particular operations and what areas can be assumed to be free of obstacles etc.

The markings are, I think, a different issue.

Obviously you have a problem with your local authority that, on the information you have given, seems to want to make an example of your friend. I'm wary of quoting law - as you have asked for - because only a lawyer familiar with your legislation can advise you on this but your link to the Canadian AIP may not be quite the same as law. In the UK there is law (called the Air Navigation Order - ANO) that covers how aircraft are operated and other aviation things. The AIP is an information document that has no status as law. But the ANO says you mustn't endanger anyone with your aircraft and if you ignore something in the AIP you may be accused of endangering someone, maybe because you didn't follow normal aviation procedures or advice in the AIP.

[guclu]

ac500u,

The ICAO documents are not like Canadian AIP. I checked once more.

Just a copy paste for you from Annex 14 Aerodromes

10.2 Displaced threshold
10.2.1 If an object extends above the approach surface
and the object cannot be removed, consideration should be
given to displacing the threshold permanently.
10.2.2 To meet the obstacle limitation objectives of
Chapter 4, the threshold should ideally be displaced down the
runway for the distance necessary to provide that the approach
surface is cleared of obstacles.
10.2.3 However, displacement of the threshold from the
runway extremity will inevitably cause reduction of the
landing distance available, and this may be of greater operational
significance than penetration of the approach surface
by marked and lighted obstacles. A decision to displace the
threshold, and the extent of such displacement, should
therefore have regard to an optimum balance between the
considerations of clear approach surfaces and adequate landing
distance. In deciding this question, account will need to be
taken of the types of aeroplanes which the runway is intended
to serve, the limiting visibility and cloud base conditions under
which the runway will be used, the position of the obstacles in
relation to the threshold and extended centre line and, in the
case of a precision approach runway, the significance of the
obstacles to the determination of the obstacle clearance limit.
10.2.4 Notwithstanding the consideration of landing
distance available, the selected position for the threshold
should not be such that the obstacle-free surface to the threshold
is steeper than 3.3 per cent where the code number is 4 or
steeper than 5 per cent where the code number is 3.
10.2.5 In the event of a threshold being located according
to the criteria for obstacle-free surfaces in the preceding paragraph,
the obstacle marking requirements of Chapter 6 should continue to be met in relation to the displaced threshold.

But may be this might be of help for you (also from An14) :

3.1.5 Recommendation.- When it is necessary to
displace a threshold, either permanently or temporarily, from
its normal location, account should be taken of the various
factors which may have a bearing on the location of the
threshold. Where this displacement is due to an unserviceable
runway condition, a cleared and graded area of at least 60 m
in length should be available between the unserviceable area
and the displaced threshold. Additional distance should also
be provided to meet the requirements of the runway end safety
area as appropriate.

Best Regards,

Guclu

[ac500u]

Thanks for everyone's replies.

Responses in Order....

Ex-DC-Driver - Regarding why. Simple put, because it is safer. Some aircraft which were built in the 50's, had numbers that were very optimistic. It was very popular in that era to juice the numbers to sell aircraft. The Ac500 is a fine example. I can't remember the exact numbers but it says you can land at gross, in something like 1100ft. It also suggests that you approach at around 65 kts. Both of these are near impossible. At gross and 65kts, the aircraft is in a full stall, not just horn, full wing drop chaos. Maybe if you hit the runway at 65 you could stop in 1100, but you might not be able to use the aircraft again. But, according to the numbers, and the 'buffer' it is perfectly legal. But, I assure you those numbers are truely outrageous. The t/o numbers are even worse. Something like 1400 at gross. Absolutely absurd. Anyone who's flown one can verify. So, in my mind, not why, but WHY NOT. The obstacle is cleared, the runway is solid, and the is 50 feet of water 4ft of the end of the runway. Which do you really think is safer?

Spitoon - Regarding changes to the displaced portion. As you described yourself, this portion is clearly allowed to be used for backtrack, takeoff, and landing roll from other direction, it's just landing that's in question. If someone was digging a hole ON ANY PART OF THE MANUEVERING AREA, there would have to be a notam, and resultant markings. It is still part of the manuevering area, irregardless of it's availability for landing.

Still very interested in any quotes from law, or even guidance books such as AIP's. I've read the ICAO standards several times, but it doesn't clearly stipulate yes or no.

Thanks again for everyone's input.

[LanFranc]

You asked for "any" legal reference. Here's one, albeit local in nature but very plain.
http://www.dot.wisconsin.gov/travel/air/docs/apt-standards.doc

scroll down, item 9

The quote:

A displaced threshold is a runway threshold located at a point other than the physical end of the runway. The portion of the runway so displaced may be used for takeoff but not for landing. Landing aircraft may use the displaced area on the opposite end for roll out

And onther....

From the FAA, Central Region - Airports Division, AIP Guide Index, Runway Commissioning, Data elements:
The link:

http://www.faa.gov/arp/ace/aip/aip-1121.cfm

Scroll down to item 51.

The quote:

The portion of pavement behind a displaced threshold may be available for takeoffs either
direction and landings from the opposite direction. This length is included in the total length of the
runway.

[ac500u]

Thanks.

Score now 2 illegal - 1 legal.

[OzExpat]

It might be a good idea to remember that, when quoting anything from an ICAO Annex, it is not law. Contracting States make it into law through their own legal processes and should notify any differences in their AIP. This might be a good place to start your research ac500u.

If there's no reference to "displaced thresholds" you might be able to infer that the national aviation laws in the particular country fully reflect the Annex 14 specifications. If so, you probably need to see what clarifying information is provided in the AIP. After checking all of that, you'll probably need to consult a lawyer who is conversant with the laws of that country.

[Groundloop]

ac500u, you use the phrase "the runway is solid". But is it STRONG enough to take the forces of a landing aircraft? Runway extensions are often built to lower bearing standards because its cheaper! How are you supposed to know what the strength of this area is? Because you have always landed on it in the past? Don't think that would stand up in court.

[ac500u]

The runway is consistent from end to end. The only put the displaced threshold markings in a few years ago.

Also, if a portion of the runway in too weak to support landing light aircraft, it would most likely be too soft to support taxiing, or stationary aircraft as well, due to prolonged times in one position.

I've never heard of pavement that can support light aircraft taxiing, but not landing. I don't mean it doesn't exist, I've just never heard of it, have you? You have any examples?

Oh, and finding a lawyer who\'s conversant with the local regulations is like finding a local rocket scientist.

[OverRun]

ac500u,

I've stuck a few displaced thresholds in during my time. Before I come out with my version of the warnings that j-t and mutt were making, let me mention the ICAO section that goes to the heart of the aircraft operation and is relevant to your request: Annex 6 — Operation of Aircraft Part 1 (8th edition):

5.2.11 Landing. The aeroplane shall, at the aerodrome of intended landing and at any alternate aerodrome, after clearing all obstacles in the approach path by a safe margin, be able to land, with assurance that it can come to a stop or, for a seaplane, to a satisfactorily low speed, within the landing distance available. Allowance shall be made for expected variations in the approach and landing techniques, if such allowance has not been made in the scheduling of performance data.

There is nothing else in Annex 6 that makes landing short illegal or legal. There are also examples in the Attachments of that Annex on how the aircraft manufacturers calculate landing distance, but while informative to read, they don’t dictate how the pilot must land the aircraft. They are presumably for standardisation and the avoidance of over-optimistic performance numbers such as you mentioned earlier.

OzExpat put a nice argument in his post above, which suggests your lawyers can take forward this short, but powerful section 5.2.11 to build the case that the flight was legal because you landed safely etc etc. The pavement strength issue is a rarity and not normally expected to crop up in displaced thresholds (but I'm not ruling it out). If the local groundstaff can drive their truck up the runway or drive the firetender up it, then it will support a light aircraft.

Now back to the warnings. I find the calculation of displaced thresholds are not easy and are somewhat counter-intuitive. We always have 3 or 4 people do the calculations, and after going around a bit, they hopefully come up with the right answer. That takes a few days to work out, and I wonder how your friend can do it so quickly while landing the aircraft. I'm sure he is aware of the obvious traps, such as:
- the highest object in the approach is not the governing obstacle for displacing the threshold
- the governing object is not necessarily visible
- the obstacle need not be present to be the governing obstacle
It is easy to land short once and get away with it, but the principle behind the design of displaced thresholds is that you can land safely every time, and I still don’t see how your friend has built longevity into his operation.

[ac500u]

Over Run,

Thanks for the informative post. Nice name by the way... somewhat appropriate for this topic.

When it comes down to safety, (and longevity) like you had mentioned, that obviously has to be taken on a case by case basis.

I would never suggest landing prior to a displaced threshold on any airport that someone wasn't extremely familiar with.

The sea level VFR only airport in question has been around for about 12 years. They decided to paint a displaced threshold on it about 6 years ago. The pilot in question has landed at this airport virtually every working day for the last 4 years. Probably more than 1000 times. The obstacle on the approach cannot be mistaken, it is a large hill approximately 2 miles on final roughly 500 ft tall. It is possible to approach over the hill, but the gradient is quite extreme. It is very easy, and common practice to turn base/final inside of the 2 miles, and thus entirely avoid the hill, the very obstacle displacing the threshold.

In this particular case, safety and longevity require landing before the displaced threshold. History at this airfield has shown that several aircraft have overrun the runway, after touching down post threshold, but none have ever over run after settling prior to.

The numbers allow several different types to land there, commonly BN2's, AC500's, DHC6's, C402(stolkit) etc. Some have gotten authority to land 208's and 228's but the numbers do not allow such.

In summary, I think in this specific case, and several others, the opposite of the theory could be valid. That is, you could get away with landing after the threshold once, but it would be safer to land before it, every time.

[Spitoon]

ac500u, I am pleased that you have gained confidence from the posts in response to your question. You clearly believe that the information that I offered, to the effect that as the pilot of a landing aircraft you may not be aware or be made aware of some activity that is taking place in an area of the aerodrome that is not available for landing, is incorrect.

Having spent the best part of 30 years dealing with such matters, I can assure you that in certain circumstances this may well be the case. For the benefit of anyone else reading this I would suggest that touching down before a displaced landing threshold is highly inadvisable. To re-iterate my earlier comment "A displaced landing threshold is the start of the runway for a landing aircraft".

[ac500u]

Spitoon,

Would you agree that the 'unavailable portion' as you've described it, is part of the Manuevering Area? If it isn't, why not? If it is, why would this area not be held to he standards of the rest of the manuevering area, such as surface integrity, clearance to position, etc?

If you need clearance to taxi on the taxiway, why would you not need clearance to move through the displaced portion? If potholes on the apron are notamed, or marked, why would they not be on the pre threshold portion? If there were some obstacle on the displaced part, wouldn't they then have to re-displace the displaced threshold temporarily to avoid the obstacle?

The quote I\'m most familiar with regarding this (from local regulations) is as follows.

MATTERS OF OPERATIONAL SIGNIFICANCE AFFECTING AIRCRAFT PERFORMANCE

The condition of the movement area and the operational status of related facilities shall be monitored and reports on metters of operational significance of affecting aircraft performance given, particularly in respect of the following.

a) construction or maintenance work;
b) rough or broken surfaces on a runway, a taxiway or an apron;
c) snow, slush, or ice on a runway, a taxiway or an apron;
d) water on a runway, a taxiway or an apron;
e) snow banks or drifts adjacent to a runway, a taxiway or an apron
f) anti-icing or de-icing liquid chemicals on a runway, a taxiway or an apron;
g) other temporary hazards, including parked aircraft;
h) failure or irregular operation of part or all of the aerodrome visual aids; and
i) failure of the normal or secondary power supply.


Spitoon, what is it that you are speculating could be taking place on this displaced portion that the pilot wouldn\'t know about?

[OzExpat]

Would you agree that the 'unavailable portion' as you've described it, is part of the Manuevering Area? If it isn't, why not? If it is, why would this area not be held to he standards of the rest of the manuevering area, such as surface integrity, clearance to position, etc?
Depending on the particular country's level of compliance with Annex 14 (including any differences they might have filed), it is possible that there could be Stopway prior to the (displaced) THR and perhaps RESA prior to the Stopway.

I have seen nothing in Annex 14 that specifies what the strength of these areas should be. As a result, in my country of operations, the Stopway is only half the strength of the RWY and, if there's a RESA, it is compacted gravel and soil, grassed over. I don't want to get into RESA too much, despite the fact that the Annex 14 specification states that it is provided for aircraft undershooting on approach, or an over-run on take-off. Many of the poorer countries do not provide RESA and this is why I don't want to discuss it in any depth.

However, the stopway is simply there to allow an additional length for an aeroplane to stop in the event of a rejected take-off, without doing any damage to the aircraft. Therefore, it is not intended to suffer the impact load associated with a landing and, hence, doesn't have to be as strong as the RWY itself.

The reality is that any airport operator that wants to save some money will use a lesser strength in the Stopway.

Now, to make this relevant to the permanently displaced THR scenario, the airport operator is not required to maintain the area prior to the THR to the same structual integrity as the RWY. Therefore, if the operator wants to save a quid, he won't bother to spend money on it as it deteriorates - short of patching potholes, etc.

I think this might suggest that you will never know the actual strength of the area before the displaced THR.

[ac500u]

If we're talking standards, rather than specifics, the pre threshold area is part of the movement area, and must me maintained as such. If it's condition deteriorates, and it becomes unfit for surface movement of aircraft, they would have to remark it with chevrons, or x's.

If we're talking specifics, rather than standards, lets take a step back to reality. We're talking about light aircraft here. Prior to there being a runway at this location there was a piece of dirt, which seemed to have enough surface integrity to support light aircraft. To throw 12 inches of pavement over that dirt, and say the first 600 ft is unfit is ridiculous.

Again, I'm in no way advocating 747's landing before displaced thresholds.


On a different note..

I found an interesting airport diagram in the UK AIP for Denham. AD 2-EGLD-1-3. It has two runways. In the section for 'local regulations' it states.......

"a public road adjacent to the aerodrome boundary crosses the approach to runway 24. Aircraft should not descend below the glidepath, nor touch down before the displaced threshold."

Now, this is a note for runway 24 ONLY, if this is infact regular law, why would it have to be stated as such? They don't quote and other 'standard regulations' in this section, nor on any other diagrams I looked at.

According to the locate authority, isn't this 'basic aviation knowledge'?? Why would it have to be listed with other irregularities??

[john_tullamarine]

Without checking back on previous posts ... I think Over run touched on this in saying that approach (and takeoff) obstacle clear surfaces sometimes relate to obstacles which aren't there ... and that includes transient vehicles which often constitute a limiting obstacle for the calculations ....

[RatherBeFlying]

Displaced thresholds are mostly there for the heavies that require a 3 degree stabilised approach from the outer marker.

As you have noted, light a/c have no problem setting up a one mile final that will also be one mile away from the hill and approximately level with it.

Perhaps somebody well connected objects to a/c turning final over his house -- not that making the turn 600' closer to the runway would make much difference to those below.

Before it was converted into a construction equipment parking area, I often flew out of a strip with the threshold 50' away from the road. When landing I looked both ways before crossing the street;)

[LanFranc]

ac500u

>>Again, I'm in no way advocating 747's landing before displaced thresholds.<<


So, I'm curious, just which aircraft DO you advocate landing before displaced thresholds? Should there be published lists? Not 747's but C172's , ok. What about ATR72's... too big? How about twin otters?

I believe you're clutching at straws trying to make the case for your friend. The fact is that no matter how many times people do something wrong, its still wrong. So far, I have been unable to find a single definition of Landing Distance Available that includes the area before the displaced threshold. I have found many, many references specifically prohibiting it.

Another question springs to mind. If you do not accept the displaced threshold as the beginning of the surface available for landing, what is your understanding of that point? Exactly where do you think its okay to plan touching down? If the unprepared surface short of the runway looks good to you, can you land there too? Is that also type specific, ie, not 747's but "light" aircraft ok?

Aviation and aviation regulation is full of grey areas. Not everything is as black and white as it should be or, in many cases, as it needs to be. In this case, the majority of posts are against landing before the displaced threshold. Technicalities aside and outside emergency situations, I think there would be very few good reasons for doing so.

[ac500u]

Lanfranc,

Please point me to the "many, many references specifically prohibiting it" which you stated in your post.

I agree that the majority of opinions in this thread favor the side of being illegal, but keep in mind, that's what they are.... opinions.

If you wish to "find a single definition of Landing Distance Available that includes the area before the displaced threshold" as you stated, see my original post with the link to the Canadian AIP which CLEARLY states that it is available. Black and white.

For some reason, you are very upset. You need to relax a little and use some common sense. You ask if I think an unprepared surface is ok to land on too. Is this question really necessary, or are you a little on tilt?

You stated that aviation regulations are full of grey areas. This is one as well. To prosecute some one for something, it generally should be black and white, or common sense.

What is the common sense reason in this case? What in this SPECIFIC case is dangerous about touching down before the threshold. Are the wheels gonna bust through the pavement? Is it possible to hit an obstacle that is 2 miles behind you?

What are the inherent dangers of touching down past the threshold? Wet runway? Bad brakes? Beta Failure? Wind shear? Deep ocean of the end? Once again, several aircraft have run off the end after touching down past the threshold. None (zero) have ever run off after touching down before.

If you relax a little and read more of the relavent posts, you'll see that I was never generalizing that it is ok the land before a threshold at any random airport. I am talking about a specific case. And in this specific case, if you choose to land past the displaced threshold everytime, it will only be a matter of time before you run off the end.

But, we are talking about black and white so again Lanfranc, PLEASE POINT ME TO THE ""many, many references specifically prohibiting it"

[Spitoon]

Ok ac500u, I'll humour you one more time. We're talking about an airport with ATC, right? ATC control what is going on on the manoeuvring area, they know about everything that's going on. They'll tell you about anything that you need to know about based on what you are expected to do (or have been cleared to do).

In the hypothetical situation that I mentioned earlier - where the displaced threshold is so far down the runway that anything on the normal/take-off threshold is outside all of the obstaclre clearance surfaces and runway strip - I could, for example allow a vehicle to cross the normal threshold...and I may not bother telling you about it. I've cleared you to land and I'm going to assume that you'll aim to land past the displaced threshold because that's the bit of runway that's notified as available for landing. In strict terms, if you land short of the displaced threshold, it's little different to landing on another runway. You wouldn't land on a different runway to the one you're cleared to land on, would you? Even if you could see there was nothing else on the runway?

As to the NOTAM thing. I'm not going to NOTAM a runway crossing. And I'm not going to NOTAM that the approach lights will be u/s for half an hour on a glorious sunny afternoon whilst some maintenance is done. Why not? Because there's ATC and I'll tell you about it if you need to know - see above about basing what you need to know on what you've been cleared to do. If it was an uncontrolled field things would be different - stuff would have to be NOTAMed because it's possible that no-one at the field will be able to tell you about it. But we're talking about an airport with ATC.

You cite the warning in the Denham entry in the UK AIP. In the UK the AIP is an information publication (I guess the title gives it away a bit), airports can put pretty much anything relevant in their entry. It's probably there because some idiot chose to ignore the markings and caused a problem.

Airmanship or good aviation practise seems rarely to be explicit in law - it's very difficult to define anyway. In the UK there is legislation - ANO articles 63 and 64 - that says you mustn't endanger the aircraft or anyone else. It's a matter of interpretation as to whether any particular action constitutes endangering and definitive interpretation is the one decided in court. I would guess that many other states have something similar. If you want to try and avoid being accused of endangering I would suggest you follow the rules as the majority interpret them.

I'm afraid I tend to agree LanFranc both with the point he makes in his latest post and with the conclusion that your friend is clutching at staws and is going to have to accept that he may be wrong on this one - and, hopefully, before he does any real damage!

[LanFranc]

ac500u

Well reasoned, very sound arguments. I believe you have a brilliant career ahead of you as a pilot. Best of luck.

Cheers

[ac500u]

Lanfranc,

There is much more to sound arguments / discussion than sarcasm, which you seem to enjoy.

You made several statements in your article, I asked you to verify their location, and you returned with sarcasm.

Is that the sound argument you were referring to?

Again, please point out the 'many, many references specifically prohibiting it' that you mentioned in your post.

It's very simple, you point them out, and I'm dead wrong.

It's doesn't seem like a difficult argument to win (if your correct).


Spitoon, I more clearly see your point, however, tend in this instance to disagree. Would you as an ATC advise anything under your control to cross any portion of a 2500ft strip, when an aircraft is landing? Not from a legal point, but practically? Imagine if it was uncontrolled, what would stop a vehicle from crossing that portion? Nothing really, but that's why we keep our eyes peeled for obstacles on landing, whether aircraft, vehicles, animals, or debris.

Again from a practical point of view. There are many aircraft which land on this runway everyday. Well, not that many, maybe 20-30 landings a day. Every single one of them touch down before the displaced threshold. They are aircraft of several countries, with pilots of several nationalities. Do you suggest that we all land before because we are all reckless? and we all constantly endangerous the lives of our passengers? I'm not saying that because everyone does it, that it's legal, but I am saying that everyone does it because it is safer.

It seems everyone is getting bothered by this. I think that everyone is seeing this from an airliner point of view as Lanfranc is. There is a world of difference between flying a A320, and a light aircraft. I've landed light aircraft on frozen lakes, beaches, and 700ft bushstrips. I still can't grasp how landing 200 ft before a strip of paint on a excellent piece of concrete is inherently unsafe. Again, that's from a practical point of view, not a legal one.

I see the practical and legal arguments as two completely different things.

I personally cannot agree that in this instance it is practically unsafe.

I would be glad to admit that it might not be 'legal' as defined by local regulations. I just can't find anywhere where it clearly states this position.

It might be 'clutching at straws' like you suggest, but I believe that can be viewed both ways. I think saying that anything is illegal with out there being a specific law, is somewhat clutching as well.

[OzExpat]

I guess the only way we're ever going to get a real and legal decision will be when (or if) the regulatory authority takes your friend to court. Decisions made there are the ony ones that truly matter. I wish your friend luck because I think he's going to need it.

[ManaAdaSystem]

Interesting discussion. Even more so when you read the "Air India off the runway in Mumbai" tread in Rumours section.

[Approaching Minimums]

Landing distance requirements, JAR-OPS 1.515

The landing distance required on a dry runway for destination and alternate aerodromes from 50ft to a full stop must not exceed:

a) 60% of the LDA for turbo-jet aeroplanes
b) 70% of the LDA for turboprop aeroplanes

Now, considering that the LDA is a runway available after threshold or displaced threshold the runway length in your case is inadequate.

I'm surprised that the local ATC has not filed the report of those pilots who land before the displaced threshold, because at least where I'm located that would be the case. It is definitely PROHIBITED.

Best Regards,
-AM-

[ac500u]

Thanks I-ford, I think you're the first to see my point.

Approaching minimums, as you quoted, as per the 'numbers' the aircraft does meet the minimum requirements, as follows......

2500ft runway, 600ft displacement, 1900 ft 'available'. 70% of 1900 is 1330. The aircraft in question requires ~1200 as per the manual. (although this is next to impossible).

I'm in full agreement that where you are it might be prohibited, but do you have any documents that clearly state this regulation? If you do, please send me a link.

Also, regarding ATC not filing reports, there is obviously a reason. Possibilities are that it's either not illegal (as in Canada), or they don't wish to close the airport. If they were to file reports on every single aircraft that lands (like I mentioned earlier, ever single aircraft at this airport lands before the displaced threshold), I have to assume that this would effectively close the airport.

I get the impression that alot of people here think that it's just one ignorant pilot landing before a displaced threshold for no reason. I assure you that is not the case. It is every single pilot, every single landing. All nationalities, all registrations. Chief Pilots, training captains, and CAA examiners. That has to be hundreds if not thousands of pilots over the years. Statistics would suggest that we can't all be ignorant psychopaths.

[manuel ortiz]

AC500 any end for the story ?