Use of runway distances

[Barnside]

I'm not a professional - just a PPL IR but I could do with some experienced feedback to the following question.

When looking up airport information, specifically runway distances, what is the relative importance of the following measurements? (my own thoughts in brackets)

LDA (presumably of critical importance?)
TORA (isn't this always the same as runway distance?)
ASDA (is this of any value without TODA?)
TODA

Thanks

[Mowgli]

Barnside:

LDA: the runway length available and suitable for the ground landing run of an aeroplane (CAP 168)

TORA: the declared distance available which has the same load bearing strength along that whole length (and breadth)

TODA: = TORA + clearway or 1.5 x TORA whichever is less.

Clearway: A clearway may have no load bearing strength and may be land or water. It is an area beyond the end of TORA which is free from obstacles which may cause a hazard to ac in flight. (i.e an area where after lift off you can safely transit to the screen height)

ASDA: = TORA + stopway.

Stopway: An area beyond the end of TORA which can be used infrequently after an abandoned take-off. i.e it is able to support the weight of an ac and should have a similar co-efficient of friction to the runway but is for occasional use only and is a cheap way of allowing heavier aircraft to utilise the runway. Hence ASDA = accelerate-stop distance available whereas TODA is used to calculate the limit for getting airborne rather than stopping.

Hope that helps!

[john_tullamarine]

A point of addition/clarification.

TORA/TORR is used for heavies to consider the requirement to get airborne before the end of the runway. TODA/TODR, on the other hand, may include some of the scheduled airborne distance over an area unsuitable for the aircraft to run its wheels along.

So, depending on the rules you are looking at, either at least 1/3 or 1/2 of the calculated airborne distance to 35ft is scheduled to occur over the last bit of the TORA.

Depending on the aircraft, runway, and ambients, this will result in either TODR (for each of AEO and OEI) or TORR (ditto) being the limiting continued takeoff runway consideration.

[Genghis the Engineer]

These may help

http://www.caa.co.uk/docs/224/ssl7.pdf

http://www.bmaa.org/006_1.pdf

G

[Barnside]

Thanks for the helpful replies. Perhaps my original request should have been better clarified. My 'day job' is running an online briefing service and we are trying to maximise the runway information we can derive from the raw data (from an ARINC compliant source).

The raw data contains (relevant to this discussion):

runway_length | character(5) |
rwy_grad | character(5) |
landing_thres_elev | character(5) |
displcd_thr | character(4) |
width | character(3) |
stopway | character(4) |

So we can display LDA and TORA.

We could display ASDA but presumably without TODA this would be pointless.

Or would presenting ASDA without TODA be of some use?

Regards to all,

[Captain Stable]

Barnside, pleased don't take this personally, but I am finding it rather worrying that you appear to be publishing these distances having deduced them from other sources without really understanding what you are doing.

This information is critical to flight safety.

The only 100% safe source for such information is the AIP. Go there. Do not extrapolate, do not interpret, do not collect $200.

[Barnside]

Dear Capt. S.

Fear not! I was trying to keep a very low profile in not wanting to use this forum to promote my company services.

Our company is one that I expect you have heard of and is a fully ICAO approved briefing service. Our data is provided by the UK Met Office and (for airfield information) Thales Avionics. Our aeronautical data feed is from the Aeronautical Services Group aka Aerad. Their data is widely used in FMS's. (We are also an approved UK AIS 3rd Party supplier and just waiting for the ADIMS feed to go live).

In the past we have not published anything more than basic runway dimensions as the majority of our users are GA pilots. Now that we have many more commercial users subscribing to our service we want to present more runway data as it is part of the data set provided by ASG.

What is in the data set was covered in my previous posting. My query was really about ASDA. My view is that presenting ASDA without TODA (that is NOT in the data set) would be pointless.

I was just seeking a view from this forum and hope this allays your fears ;-)

If you want to email me off-forum I can fill in more of the background.

Regards,

[Genghis the Engineer]

Leaping to the defence of Barnside (and frankly, I've no real idea who he is or what company he works for), virtually all of us routinely work from data that is not directly from official sources.

Obvious examples are various VFR flight guides, after-market aircraft manuals, commercial checklists, checklists and reminder cards produced by flying schools - the list is far longer than the list of "official" data such as the AIP or manufacturers approved data.

We do rely upon people like this - and their products - to make our lives liveable. And equally if an aviation professional can't ask apparently "daft" questions on Pprune, then I'm not quite sure what it's here for.

G

[john_tullamarine]

For heavy aircraft operations the simple answer is that the pilot (or operations engineer) needs

(a) TORA to determine the TOR-limited TOWs (AEO and OEI)
(b) TODA to determine the TOD-limited TOWs (AEO and OEI)
(c) ASDA to determine the ASD-limited TOW
(d) LDA to determine LD-limited weights both for departure, in the case of a return, and destination/alternate.
(e) either discrete obstacle data in the takeoff splays OR
(f) obstacle clear surface data referenced to runway distances.

Runway slope affects all the above calculations and width usually is linked to survey standards for obstacle data.

Generally, the ops engineer does the sums to seek maximum accuracy and optimum weights from flight manual data while the pilot runs a simplified calculation, often from simplified ops manual recasts of the flight manual data. This is not to suggest that the pilot cannot do the more involved calculation .. only that the time available normally precludes his/her doing that.

It is not a matter of trying to prioritise these various data.... they are ALL necessary as ANY one of them can result in the limiting TOW for the particular operation on the particular day. Each calculation is done essentially in isolation from the others and the results are then ranked to determine the most limiting case .. ie the case which results in the minimum TOW permitted.

[bookworm]

I think the issue is this:

The data contains runway length and stopway data, but no clearway data. Since a stopway is always a clearway, one can assume that the TODA >= ASDA.

Barnside can display TORA and ASDA, and the user can make the assumption that TODA = ASDA. If, with that assumption, case (b) is the most limiting case, the user can make further enquiries in the appropriate AIP to discover if clearway is available and the TODA is, in fact, greater than ASDA.

If this were a rare event, displaying the TORA and ASDA data would be a useful tool for a coarse indication of runway availability. If it were usually the most limiting case, there would be little point in displaying the data, because the user would almost always have to make the extra checks, even for a coarse indication.

There's a similar issue with ASDA. Since a runway is always a stopway, one can assume that the ASDA >= TORA. If, with that assumption, case (c) is the most limiting case, the user can make further enquiries in the appropriate AIP to discover if stopway is available and the ASDA is, in fact, greater than TORA.

If this were often the most limiting case, displaying the TORA and ASDA data would be a useful tool for a coarse indication of runway availability. If this were a rare event, displaying the ASDA would probably be a waste of space, as TORA (runway length) would be all the user needed in most cases.

If the most limiting case is usually (e) or (f), there's not a lot of point in displaying any of the data!

In the much simpler case of light aircraft ops, I know that TORA is all I need to look at on the first pass. If it's close, I'll hit the books and find out exactly what the TODA is, and exactly what I require. I'm spared the need to think about ASDA, since if an engine fails at an inopportune moment, I'll be landing on the runway, stopway, clearway or freeway regardless. :)

So the question is, what's the limiting factor in most cases for 'heavy aircraft operations'? Are (b) or (c) often the most limiting?

Hang on...

Since a stopway is always a clearway...

But that's not true, is it? Clearway has to be 152 m wide. Stopway doesn't. Heathrow runway 23 is a good counter-example.

So reading it as

Barnside can display TORA and ASDA, and the user can make the assumption that TODA = TORA. If, with that assumption, case (b) is the most limiting case, the user can make further enquiries in the appropriate AIP to discover if clearway is available and the TODA is, in fact, greater than TORA.

does it still make sense?