View Full Version : Close-in obstacles limiting takeoff

Cloud surfer
3rd Oct 2005, 15:51
I'm currently looking at performance figures for a turboprop, and in that regard reviewing the official Aerodrome Obstacle Charts (type A) for a specific airport.

Within the initial "splay" sector (90m [or 60+ 1/2wingspan] each side of threshold + 0.125D), I have a few masts and man-made obstructions (buildings) which, if cleared by 35', cause in my view an unnecessary high 2nd segment net climb requirement - hence a large payload penalty.

I'm aware that I can disregard "visual" obstacles outside of 300m, but these obstacles (they are at the outer edges of the splay) are closer than that, but still along the outer edge of the "splay". It would seem reasonable for me to set a minimum visibility / cloud base restriction on this departure, instructing aircrew to remain visual with the obstacles in case of engine failure and avoiding them; and then "removing" these from the obstacle list which limit my climb requirment.

However, I can find no references in JAR-OPS or any other legislation which give me judicial acceptance of this. Any ideas?

3rd Oct 2005, 16:53
Cloud surfer,
this is JAR OPS requirements for the class a airplanes:
AMC OPS 1.495(d)(1) & (e)(1)
Required Navigational Accuracy
See JAR-OPS 1.495(d)(1) & (e)(1)
1 Flight-deck systems. The obstacle accountability semi-widths of 300 m (see JAR-OPS 1.495(d)(1))
and 600 m (see JAR-OPS 1.495(e)(1)) may be used if the navigation system under one-engine-inoperative
conditions provides a two standard deviation (2 s) accuracy of 150 m and 300 m respectively.
2 Visual Course Guidance
2.1 The obstacle accountability semi-widths of 300 m (see JAR-OPS 1.495(d)(1)) and 600 m (see JAROPS
1.495(e)(1)) may be used where navigational accuracy is ensured at all relevant points on the flight
path by use of external references. These references may be considered visible from the flight deck if they
are situated more than 45° either side of the intended track and with a depression of not greater than 20°
from the horizontal.
2.2 For visual course guidance navigation, an operator should ensure that the weather conditions
prevailing at the time of operation, including ceiling and visibility, are such that the obstacle and/or ground
reference points can be seen and identified. The Operations Manual should specify, for the aerodrome(s)
concerned, the minimum weather conditions which enable the flight crew to continuously determine and
maintain the correct flight path with respect to ground reference points, so as to provide a safe clearance
with respect to obstructions and terrain as follows:
a. The procedure should be well defined with respect to ground reference points so that the track to
be flown can be analysed for obstacle clearance requirements;
b. The procedure should be within the capabilities of the aeroplane with respect to forward speed,
bank angle and wind effects;
c. A written and/or pictorial description of the procedure should be provided for crew use;
d. The limiting environmental conditions (such as wind, the lowest cloud base, ceiling, visibility,
day/night, ambient lighting, obstruction lighting) should be specified.
[Ch. 1, 01.03.98]
IEM OPS 1.495(f)
Engine failure procedures
See JAR-OPS 1.495(f)
If compliance with JAR-OPS 1.495(f) is based on an engine failure route that differs from the all engine
departure route or SID normal departure, a “deviation point” can be identified where the engine failure route
deviates from the normal departure route. Adequate obstacle clearance along the normal departure with
failure of the critical engine at the deviation point will normally be available. However, in certain situations
the obstacle clearance along the normal departure route may be marginal and should be checked to ensure
that, in case of an engine failure after the deviation point, a flight can safely proceed along the normal

For performance calculations regarding class B airplanes:
IEM OPS 1.535
Obstacle Clearance in Limited Visibility
See JAR-OPS 1.535
1 The intent of the complementary requirements JAR-OPS 1.535 and Appendix 1 to JAR-OPS
1.430 sub-paragraph (a)(3)(ii) is to enhance safe operation with Performance Class B aeroplanes in
conditions of limited visibility. Unlike the Performance Class A Airworthiness requirements, those for
Performance Class B do not necessarily provide for engine failure in all phases of flight. It is accepted
that performance accountability for engine failure need not be considered until a height of 300 ft is
2 The weather minima given in Appendix 1 to JAR-OPS 1.430 sub-paragraph (a)(3)(ii) up to and
including 300 ft imply that if a take-off is undertaken with minima below 300 ft a one engine inoperative
flight path must be plotted starting on the all-engine take-off flight path at the assumed engine failure
height. This path must meet the vertical and lateral obstacle clearance specified in JAR-OPS 1.535.
Should engine failure occur below this height, the associated visibility is taken as being the minimum
which would enable the pilot to make, if necessary, a forced landing broadly in the direction of the
take-off. At or below 300 ft, a circle and land procedure is extremely inadvisable. Appendix 1 to JAROPS
1.430 sub-paragraph (a)(3)(ii) specifies that, if the assumed engine failure height is more than
300 ft, the visibility must be at least 1500 m and, to allow for manoeuvring, the same minimum visibility
should apply whenever the obstacle clearance criteria for a continued take-off cannot be met.

AMC OPS 1.535(a)
Take-off Flight Path Construction
See JAR-OPS 1.535(a)
1 Introduction. For demonstrating that an aeroplane clears all obstacles vertically, a flight path
should be constructed consisting of an all-engine segment to the assumed engine failure height,
followed by an engine-out segment. Where the Aeroplane Flight Manual does not contain the
appropriate data, the approximation given in paragraph 2 below may be used for the all-engine
segment for an assumed engine failure height of 200 ft, 300 ft, or higher.
2 Flight Path Construction
2.1 All-Engines Segment (50 ft to 300 ft). The average all-engines gradient for the all-engines
flight path segment starting at an altitude of 50 ft at the end of the take-off distance ending at or
passing through the 300 ft point is given by the following formula:

Y300 =0•57(YERC)/1 + (VERC*2 – V2*2) / 5647

NOTE: The factor of 0.77 as required by JAR-OPS 1.535(a)(4) is already included where:
Y300 = Average all-engines gradient from 50 ft to 300 ft
YERC = Scheduled all engines en-route gross climb gradient
VERC = En-route climb speed, all engines knots TAS
V2 = Take-off speed at 50 ft, knots TAS
(See IEM OPS 1.535(a), Figure 1a for graphical presentation)
2.2 All-Engines Segment (50 ft to 200 ft). (May be used as an alternative to 2.1 where weather
minima permits) The average all-engine gradient for the all-engine flight path segment starting at an
altitude of 50 ft at the end of the take-off distance ending at or passing through the 200 ft point is given
by the following formula:

Y200=0 51(Yerc )/1 (Verc*2 – V2*2 ) / 3388

NOTE: The factor of 0.77 as required by JAR-OPS 1.535(a)(4) is already included where:
Y200 = Average all-engines gradient from 50 ft to 200 ft
YERC = Scheduled all engines en-route gross climb gradient
VERC = En-route climb speed, all engines, knots TAS
V2 = Take-off speed at 50 ft, knots TAS
(See IEM OPS 1.535(a), Figure 1b for graphical presentation)
Hope it could help. Sorry got a bit too long.

Cloud surfer
3rd Oct 2005, 18:43
Thank you for the post. I'm dealing with class A performance, and have the paragraphs from subpart G (amd.9) referenced above beside me.

Can I infer that you mean there is a difference between 2.1 and 2.2 in AMC OPS 1.495(d)(1) & (e)(1)?

That the obstacles/external references mentioned in 2.1 lie outside the 300m (600m w/ bank) area, while the obstacles and/or ground reference points in 2.2 are inside the 300/600 or .125D splay area?

Or, is 2.2 just a clarification of 2.1? The way I'm understanding it, 2.2 just expands the text of 2.1.

That is the essence of my question.

3rd Oct 2005, 22:22
Cloud surfer,
Hmm I quite didnt get your point.
We have to differ between:
obstacle considerations within take off path such as:
¡§JAR-OPS 1.495
(d) For those cases where the intended flight path does not require track changes of
more than 15 DEG, an operator need not consider those obstacles which have a lateral
distance greater than:
„300 m, if the pilot is able to maintain the required navigational accuracy
through the obstacle accountability area, or
„600 m, for flights under all other conditions.¡¨
¡§JAR-OPS 1.495
(e) For those cases where the intended flight path does require track changes of
more than 15DEG, an operator need not consider those obstacles which have a lateral
distance greater than:
„600 m, if the pilot is able to maintain the required navigational accuracy
through the obstacle accountability area, or
„900 m for flights under all other conditions.¡¨

And the way to determine the required Nav. Accuracy as follow:

The Required Navigational Accuracy is defined in AMC-OPS 1.495. It can
either be obtained via navigation aids, or by using external references in case of
Visual Course guidance (VMC day flights).

I would say the 2.2 is the explanation derived from 2.1.
However JAR and FAR are slightly different in handling this issue as follow:
JAR doesn¡¦t specify lateral separation from the obstacles within the funnel where as FAR does, namely:
¡§FAR 121.189
(d)(2) No person operating a turbine engine powered transport category airplane may
take off that airplane at a weight greater than that listed in the Airplane Flight Manual
[¡K] that allows a net takeoff flight path that clears all obstacles [¡K] by at least 200
feet horizontally within the airport boundaries and by at least 300 feet horizontally
after passing the boundaries.¡¨

If you are interested in detailed information please read ¡§getting to grips with aircraft performance¡¨ a document I would recommend to everybody. I have used a lot out of this DOC.
Read it your self you might understand it different way.


4th Oct 2005, 08:13

If you're planning to use this aerodrome for a commercial flight, presumably it's going to benefit the aerodrome. How about asking them to remove or change the position of the obstructions? If they can't be moved, how about making other changes on the aerodrome, such as a starter extension?

We added a mere 137 metres to the eastern end of 26L. That enabled operators to lift tonnes more over Russ Hill, an obstruction to the west of LGW. Paid for itself in no time!

The Odd One

ps one American pilot suggested another solution involving the use of Caterpillar tractors - 'get come Cats up there and take that hill out!'

A bit drastic, we thought.

4th Oct 2005, 14:22
Reminds me a bit of when Orion got the B 737-300 (we were the launch customer in fact) which was not too hot (no pun intended) on climb wrt obstacles on take off etc.

Corfu RW 17 was a bit limiting due to the small island off the end with some trees. We tried to persuade them to chop the trees down but they wouldnt play ball! We also tried to argue that the people who walked across the causeway just off the end were "frangible" but once again they wouldnt buy that idea either.

Full marks to out Nav Dept Manager, John Jones (ex Flight Nav but long retired now, I think) who predicted well before we got the a/c that we would be limited ex CFU!

5th Oct 2005, 00:31
.. it always amazes me that any company buys any bit of kit .. aircraft or whatever ... without doing all the due diligence homework ahead of the CEO's putting his moniker on the dotted line ... good way to go broke if you don't do it ...

Alex Whittingham
5th Oct 2005, 08:44
Following on from TheOddOne's suggestion, when the RAF had to clear close in obstacles and they were not field length limited they occasionally employed a device where the field length was notionally reduced by a few hundred metres. This reduced the FLL weight but moved the end of the TODR back, away from the obstacles, thus improving obstacle clearance. Might work for a turboprop?

5th Oct 2005, 11:00
.. which is what one does, in effect, in a conventional AFM analysis ... ?

Alex Whittingham
5th Oct 2005, 11:23
Not in all. I've used manuals that start the obstacle domain at the end of the TODA and take no account of the effect of reduced TOM on the start point of the domain.

5th Oct 2005, 12:46
.. yes .. but .. one can vary the TODA etc at will in a consistent manner .. the effect is only to displace the obstacle domain further from the "adjusted" runway head. Just because the AFM is designed with a particular slant is no reason to use it precisely in the manner envisaged ....

Same thing, if you will, as telling the AFM that we are looking at a runway with a displaced runway head .. ?

Cloud surfer
6th Oct 2005, 07:36
Thanks for all your input.

I've arrived at the same conclusion as stated in the last couple of posts by John and Alex; namely taking the actual TODistance provided by the AOM performance chart and starting the obstacle calculations from that distance, instead of from the end of the published TODA (in the cases where by actual TOD is less than the available.) This will reduce the net climb gradient requriement by quite a bit for close-on obstacles.

The only problem is that my (0,125D) splay also increases in width compared to the "old" splay, so a slightly larger obstacle assesment area comes into consideration.

The whole operation allows me to "balance" the weight restrictions of 2nd segment climb with the weight restrictions on TOD.

And I guess we all agree (as a final conclusion to the inital problem) that no obstacles within the 0,125D splay up to a width of 300m (or 600m in bank) can be "ignored" or left out of the 2nd segment net climb requirements, no matter how visible, described, flood-lighted or flourescent colored they are? (in JAR-OPS)


Cloud surfer

6th Oct 2005, 09:42
Yes, indeed, the splay is then "beyond" the end of the presume TODA .. however, this is no different to the case where the takeoff is not distance limited ... is it not ?

6th Oct 2005, 12:35
Yes indeed it doesn’t matter if the take off performance isn’t field limited. It just shifts towards the actual TOD, reducing the required climb out gradient. However it makes sense to do it this way if there’s no problem with the whole range of take off weight up to MAX. If there’s a problem with upper range take off weights, a balanced field take off performance calculation is the preferred method, provided there’s a clearway.
Cloud surfer, just to clarify it. There might have been a misunderstanding.
Regardless of the navigation method you choose, you, as an operator, must consider all obstacles within the funnel. You must ensure as well, regardless of nav. Method, that you will clear all obstacles by 35 ft vertical distance, based on NET gradient and one engine case for given weight and environmental conditions.
The best way to do it in my opinion:
USAGE OF RTOM, if available.
Cheers. :8

6th Oct 2005, 23:31
"If there’s a problem with upper range take off weights, a balanced field take off performance calculation is the preferred method, provided there’s a clearway"

Now that statement has confused the issue ... would you care to elaborate a tad ?

Cloud surfer
7th Oct 2005, 07:11
Popay; no disagreement here... SE net climb gradient must clear all obstacles by 35'. When all the fans are running, there are no problems.

AS far as VMC departures go, there are situations where a visual departure will allow a higher MTOM, but these are then associated with distant obstacle (4th segment) climb, where it may be necessary to maintain a 300m / 600m corridor width instead of 900m due to difficult topography. (Take northern norway as an example.) However; these must be published and depicted in accordance with, as you've earlier stated, JAR-OPS 1.495(d)(1) & (e)(1). :ok:

Cloud surfer

Ignition Override
7th Oct 2005, 08:10
Popay: do pilots in Northern Europe have to think through these climb criteria when they do flight planning? Or to earn a specific license? Can it be that insane? As somebody said, it is hard to imagine sending you where there is no SID or departure info, or Jeppesen approach charts. Do you guys operate flights to such airports on a schedule? This is why we have Dispatchers, and even all the regionals here have been under Part 121 for about ten years, requiring actual Dispatch, instead of just Flight Following.

A USAF C-130 crashed during climb-out years ago in Jackson Hole, WY, partly due to the ludicrously compressed written (military) 'NOS' info about how to fly the departure. Of course the dead Aircraft Commander was blamed. It is quite a paragraph of radial this, radial that... gibberish horses**t. There was nothing simple or logical, and nothing graphic, as we have in our Jeppesens for Montana etc. There was a chartered Learjet which attempted a circling approach, AT NIGHT(!), at Eagle Colorado years ago, and they must have had Jepps, but they apparently knew nothing about the mountains :ouch: . Our 757 crews receive very specialized training each year, just for EGE! Some captains avoid the airport (I might avoid it and LAX...).

On a different note, why is our military to cheap or bureaucratic to convert to Jeppesens? Is it job security for the NOS people? I politely asked an officer, via e-mail, years ago at AMC (formerly MAC) headquarters at Scott AFB, and the answer was total bureaucratic baloney.:rolleyes:

7th Oct 2005, 10:23
john_tullamarine, well as earlier agreed TOW isn¡¦t RWY limited, but was climb limited. The actual funnel starts at the actual TOD, which might be way before the end of TODA for the given weight and prevailing conditions, if the TODA is significantly higher then required. Therefore shifting the actual TOD over the TODA, which is TORA+CLEAR WAY, will lead to increased V1/Vr & V2/Vs ratio resulting in:
An increase in MTOW limited by
First segment
Second segment
Not influencing the MTOW limited
by the:
Final takeoff segment

Maximum Takeoff Weight
For a given V2/VS ratio, it is possible to find
an optimum MTOW and its associated optimum V1/VR ratio.
For each V2/VS ratio comprised between V2/Vsmin and V2/Vsmax, such a
determination is carried out. In the end, the highest of all the optimum MTOWs and
associated optimum V1/VR is retained. It therefore corresponds to an optimum V2/VS
ratio. The result of the optimization process is, for a given runway and given takeoff
Result of the optimization process
The highest possible MTOW
The optimum V1/VR ratio
The optimum V2/VS ratio
The same result could be achieved using the derated thrust method if the TAKE OFF would be RWY limited:
A reduction in the minimum control speeds sometimes generates a takeoff
performance benefit (higher MTOW) when taking-off on a short runway. Indeed, the
decision speed V1 is the maximum speed at which it is still possible to reject the
takeoff and stop the aircraft within the runway limits. Nevertheless, V1 must be
greater than VMCG, and the Accelerate Stop Distance is often the most constraining
limitation on a short runway. A reduction of the VMCG can then permit a reduction of
the ASD for a given takeoff weight, and lead to better takeoff performance when the
MTOW without derate is ASD/VMCG limited.

Ignition Override,
To answer your question you need to refer to FAR. Dependable on art of operation under FAA dispatcher and commander bear the joint responsibility for the safe conduct of the flight. It¡¦s not the case under JAR. Under JAA the dispatcher doesn¡¦t bear the responsibility for the flight safety, he only provides necessary information. In fact many companies don¡¦t even have a dispatch department, but performance engineering dep.
I recall a flight from CUN to MSP where we had to divert to Loredo in Texas and that one was uncontrolled airport by night with visual approach and departure, but calculated performance. It wasn¡¦t a scheduled flight, but it happened quite often due to customs operating hours. So as you can see you might fly to the airdromes without IFR charts and then it¡¦s your responsibilities as a commander to ensure obstacle clearance.

7th Oct 2005, 10:47
I think I can follow most of your argument .. but where does the BFL consideration before come into it .. ?

7th Oct 2005, 11:46
If the actual TOD<TODA=ASDA the field is balanced, but not used in full length.
Therefore using the full length or balanced field calculation will possibly allow you to increase your TOW, for the reasons mentioned above.

7th Oct 2005, 12:03
.. methinks you should revisit the definition of BFL, good sir .. and I still fail to see what your point might be ?

7th Oct 2005, 18:37
john_tullamarine, ok i think i got your point. I indeed shouldn't have used the term balanced field. I thought about optimizing V1/Vr & V2/Vs for different Flap settings and as consequence possible usage of the full TODA with lower flap settings. I have associated it with BFL because the MAX TOW would be achieved with optimum Flap setting, optimum Speeds using the full length, rather then using higher flap setting and not the full length, if the take off is obstacle limited.
I hope i have regained some of your credit.

8th Oct 2005, 03:19
Bro' .. we all on the same side .. no sheep stations at stake here.

What you are doing is a normal performance analysis for a given runway .. ie juggle about with the numbers until you get a combination of weight, flap, and overspeed which fits in with the runway and obstacle data and gives you the maximum RTOW ("optimise the RTOW" in ops engineering speak).

Almost invariably, this means an unbalanced field length takeoff.

Well done, good sir. Pass "GO" and collect $200.

12th Oct 2005, 14:58
Somebody in this post mentioned the Required Navigational Accuracy as defined in AMC-OPS 1.495.

As anyone looked into it in any detail. It is my understanding that today, no aircraft meets the requirements (IMC).

Comments plz

Cloud surfer
28th Oct 2005, 14:25
Seems they're getting tired of going around from 3000' AGL.....


28th Oct 2005, 17:25
Contrary to what's been stated here, unless you're turing before the endo of the TODA, the splay does not change for changes in TOD. It is assessed only from the TODA.

JAR-OPS 1.495(a)

An operator shall ensure that the net take-off flight path clears all obstacles by a vertical distance of 35 ft or by a horizontal distance of at leat 90 m plus 0.125 x D, where D is the horizontal distance the aeroplane has travelled from the end of the take-off distance available or the end of the take-off distance if a turn is scheduled before the end of the take-off distance available.

I wouldn't want to have to re-compute the splay for every takeoff.

28th Oct 2005, 23:20
... one of the head scratching inconsistencies in the system ... it presupposes that one can track the centreline for a low vis takeoff until the splay commences .. which can be a bit difficult in older (non FMS) jets with significant deck angles. So far as turns are concerned, it would be very unusual to schedule a turn before runway head.

In practice, a sensible ops engineer will look at this problem and figure out a way to reduce the off centreline tracking risk in the case of a long runway with significant obstacles for a takeoff by a smaller aircraft .... this might well be a matter of generating a more conservative trapezoid from a convenient mid runway position if the case dictates.

Above all, blind compliance with the rules is not always a good thing ... one should consider that the rules give a baseline for commonsense to be applied .. same thing applies for the design standards. That is to say, there are occasions where the rules should be seen to be inadequate for the requirements of reasonable risk management and should be modified conservatively to reduce risk ....

Ignition Override
29th Oct 2005, 06:38
Popay- I know a pilot who might have worked for your (previous) company. He will probably get laid-off again, along with almost 400 other pilots who were recalled here just last winter. He flew a smaller Airbus.

29th Oct 2005, 07:29
donstim, to cover the problem with the turn, there's a min. turn alt. 400 ft for the BUS. Om stipulates the height for turn as well e.g. MSA for IFR or 500 ft VMC.
Ignition Override, yea man not the best time in the industry right now i guess. PM me the guys name please.

29th Oct 2005, 08:39
JT -- I was just trying to correct an erroneous statement. Didn't mean to imply that "blind compliance" with the rules is always the prudent thing to do. On the other hand, if you can't follow a track within a 200 foot half-width until the end of the TODA, maybe piloting isn't your strong suit. :O

Popay and JT -- I wasn't trying to point out any kind of a problem with turns -- just being complete as far as what the rules require. Certainly turns before the runway end are rare, but they may be appropriate (especially over clearway) in certain circumstances.

30th Oct 2005, 08:37
.. from more than a few sessions in back of the sim, give a chap an IMC failure with a little bit of crosswind and no track guidance ... and centreline tracking becomes more than a little problematic ...

No sheep stations at stake in these discussions .. so please don't think I am being critical of your comments.