take-off flight path

[Winston]

The straight take-off flight path extends to 30nm and 900m either side of track but what obstacle clearance does it give. The only reference i can find is 35ft clearance up to 1500ft for the net with 0.8% increase for the gross.

[oldebloke]

Initial ostacle clearance should meet a 1.25 degree plane(angle).
The usual Takeoff gradients should meet the initial plane(35' to 400'@2.4%..400'to 1500'@1.2% etc)..The next climb requirement is to meet 200' per nautical mile to follow the SID:ok:

[Winston]

Thanks. But if you do not follow the SID but instead climb straight ahead (If there is no engine out procedure) the straight take-off flight path starts 90m either side of the upwind runway threshold and extends to 900m either side of the extended centre line out to 30NM. If the aircraft remains within that area what obstacle clearance is assured?? Thanks a lot for your reply so far.

[john_tullamarine]

(a) keep in mind is that there are different standards for the trapezoid depending on jurisdiction and class of operation.

(b) the calculated net flight path clears the obstacle profile by 35' straight (50' turning). This is an artificial construct and it is a bad hair day if an aircraft were to be near to the NFP once the climb is established ...

(b) the (presumed) gross (which is usually less than what the typical aircraft achieves) to net gradient decrement gives an increasing clearance to the third (acceleration) segment. Then the two calculated flight paths parallel. However, the gross to net decrement in gradient readily converts to a reduction in thrust and acceleration. This reduction is applied to the net third segment distance so that, at the end of the third segment, the gross to net clearance has become a significant figure.

As to what the ACTUAL aircraft clearance on the day might be .. provided the pilot is flying the bird with a bit of skill and care, the aircraft should do a bit better than gross - it is presumed that the plane is flown with the intent of keeping the AEO profile above the OEI profile .. otherwise bets are off if one dies. Add to that the observation that very few failures occur near V1 ....

However, one needs to be very careful if the aerodrome is in tiger country and the OEI procedure is based only on a V1 failure .. some companies do this and it is presumed that the crew .. somehow and miraculously ... work out what to do if one quits during the climbout if the SID is different to the V1 OEI escape track ...

[Max Angle]

provided the pilot is flying the bird with a bit of skill and care, the aircraft should do a bit better than gross Better than NET surely?.

[john_tullamarine]

.. no ... better than gross (that's gross OEI .. not gross AEO).

Especially once we are a bit down the trail, say at the third segment ... if one is at or near the net calculated flight path .. then one is NOT having a good day .. that's why, pilot wise .. we are normally much more worried about critical obstacles early in the second segment .. as the gross to net fudge factor hasn't had sufficient distance to give one a decent pad.

You don't actually fly 35' above the obstacles once you are getting a little away from the runway .. although you might be quite close to that sort of clearance at the start of the second segment ...

The net profile is degraded to address a range of concerns which can cause the aircraft to perform worse than one might anticipate .. there is NO intention that the aircraft ought to come anywhere near the net profile, although it might well do so if all the adverse things line up against the pilots .... turbulence is a big out of left field thing .. one ought not to expect anything if it is bumpy.

A well-known performance man from years ago used to opine that the net path might be achieved as a 1 in a quarter million chance during a continued OEI takeoff .. I was never too sure where he came up with that figure .. but it gives you some sort of idea of the way things are intended to work ...

[411A]

...as I personally found out one night ex-DHA in a B707 freighter, with all four a turnin', never mind one failed.
Had the pallets weighed upon arrival...13T too much.
Big pencil whipping of the loadsheet by the handling agent.:yuk:

[john_tullamarine]

Likewise ... I can recall an F27, wet power, on two .. just making something like 200 ft/min for quite some time after a takeoff in warmish conditions ... and that was NOT overweight .. but we did love the dogwhistle.

If goes without saying, I should have thought, that the AFM predictions go out the window if the basis on which they are made are false ... like being umpteen tons (tonnes for the younger folk .. and I still think in slugs and such, as well) overweight .. not nice.

[idg]

Interesting discussion!

JT,
Presumably still not enough 'pad' in the 3rd sector to prevent GPWS going off?

Have always wondered (since we operate in 'Tiger Country') whether we could expect this. Fortunately we do not operate at RTOW for most of the runways with special OEI procedures and would therefore have more margin with TOGA used.

[Old Smokey]

As john_tullamarine indicates, jurisdictions vary, and obstacle databases vary. In Australia, for example, the obstacle analysis in the 'public domain' (RDS) does not extend beyond 15000 M (8.1 nm), after that, or after 30 nm if your obstacle database goes there (sounds like Jeppesen), you're on your own. Many, many 3rd segments go beyond 30 miles, and there you are, 2000 feet below MSA and past the arrow head at the end of your OEI procedure.

The only legimitate, safe, and moral OEI procedures are those providing lateral and vertical obstacle clearance all the way up to MSA, whereafter the operating pilot may then operate within the normal PANS-OPS (TERPS) obstacle clearance limits. It's entirely 100% achievable and possible, I do it every day.

Regards,

Old Smokey

[john_tullamarine]

Re GPWS .. this came a long time after the segmented takeoff approach (ICAO PAMC dating back to the 50s as I recall) so the two are not integrated unless the performance engineer considers the GPWS envelope in designing the escape procedure. If, for normal AEO departures, which are way above the OEI profile, you get a warning, then you most likely will do so OEI as well. No reason why you can't draw this to the attention of your ops engineering folks so that the departure can be reviewed for a less stressful pilot experience OEI.

[autoflight]

Very nicely put, Old Smokey

[faq]

Thanks John_T and others, but what are some of these abbreviations? The ones I understand are below and for the benefit of those who don’t.

SID: standard instrument departure
NFP: net flight path
AFM: aircraft flight manual
RTOW: regulated take off weight
TOGA: take off go-around power
MSA: minimum safe altitude
GPWS: ground proximity warning system

These I don’t understand. Please could someone decipher: -

AEO: ?
OEI: ?
PANS-OPS (TERPS): ?
- Specifically what is the TERPS section or relevance?
(RDS): ?
(ICAO PAMC): ?

Lastly, when an aircraft is new, flown under ideal conditions by a pilot who flies the aircraft exactly according to the procedure in the aircraft flight manual (AFM), the aircraft will perform to net (or is it gross?) performance.

Taking into account degradation in aircraft performance, less than optimum flight conditions and variation in pilot technique, manufacturers – or is it regulating authorities - then produce gross performance figures (or is it net?) and this is intended to reflect the performance of the average aircraft in service.

- Which is correct?

Thanks

faq

[square leg]

AEO: All Engines Operating/All engine operation(s)
OEI: One Engine Inoperative
PANS-OPS: Procedure for Air Navigation Services (ICAO document 8168)
TERPS: Terminal Instrument Procedures (FAA-USA)

The major differences between PANS-OPS and TERPS are holding speeds and circling procedures.

I don't yet know what RDS or PAMC is/are, but will look them up now.

Regards,

[Old Smokey]

RDS = Runway Distance Supplement, an Australian publication.

Regards,

Old Smokey

[john_tullamarine]

RDS - AIP ERSA RDS (this may be a little bit Australian if you are in another country)

AIP - Aeronautical Information Publication (the normal means by which a State publishes how it complies with its operational responsibilities, declares non-compliance with ICAO requirements, and is the basic source of routine information for pilots when going about their flying activities.

ERSA - Enroute Supplement Australia. Provides a majority of cockpit level information relating to flights around Australia and is an essential adjunct to flight planning and operation

RDS - Runway Distance Supplement to ERSA. Provides information relating to aerodrome runways, especially distances and obstacle clear surface slopes for takeoff.

PAMC - Provisional Acceptable Means of Compliance. The PAMC referred to started the idea of pre-planned segmented takeoff climb performance for large aircraft. Long time since I have seen anything to do with it. If not the first to comply with this, one of the earliest recertifications was the F27 and this all happened a LONG time ago when I were still a lad in grey school knickers. Just think historical antecedent to FAR/JAR 25.

Climb - gross is the reasonable minimum gradient you should see in the real world OEI situation - provided the aircraft is flown reasonably well. The gross to net margin is a notional fudge factor to provide some margin for this and that - but doesn't consider turbulence or inversions which are a worry if you are out in such conditions and one quits on you. I wouldn't worry too much about fleet averages and the like - that's certification backroom stuff from previous eras. You might find some useful gen in the FAA Flight Test Guide (http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/C2614E27B49BF38686256BA300696689?OpenDocument).

It certainly is not impossible to see an aircraft down in climb somewhere near the certification net performance ... but you are having a REAL BAD hair day if you are faced with that circumstance.

The OEM does the work ... then they have to sell the certification product to the regulatory authority to get the Type Certificate.