Ah yes obstacle limited is indeed the correct term.

John, I think you should read my previous post before you sent me to the schoolbenches.

Yes mutt I mixed up climb with obstacle, i was thinking of it as 2nd segment limited and thought of it as a climb limit which is solely the case for the minimum regulatory climb gradient. When there are obstacles in the 2nd segment requiring a higher gradient it is an obstacle limit.

So I mixed the 2 up.

So what I meant to say is that within the WAT limits the aircraft will always achieve 2,4%.

However I'm not the one stating that the 2,4% regulatory gradient offers a 1,6%
Net flight path. In my view both are completely seperate. One is certifying minimum the other based on the actual performance and weight on the day that considers local obstacles.

I presume you realise that this is an instant value and not a constant value, so you will achieve 2.4% at the start of the climb but it can be less at the end of the 2nd segment.... Surprised? So was I when Mr Boeing stated it :)


Look at far 25.111 and 115 and see if you still think the same thing about the climb gradient.

Mutt

before you sent me to the schoolbenches

Apologies .. not the point of my comment. The main concern is to avoid the new chums getting confused along the way.


In my view both are completely seperate

Not quite the case. The 2.4% gross data should be viewed as an actual minimum climb capability or even marginally less than that obtained. The 1.6% is the expected gross data reduced by 0.8% to provide a reasonable, real life, margin for obstacle etc., clearance calculations.

Thus, gross approximates what you expect to see on the gauges while climbing out while net is the calculated data upon which one bases the obstacle clear flight profile for preflight calculations.

The two are inextricably linked.


but it can be less at the end of the 2nd segment

Used to cause heartache in Australia where the local rule book required that the performance be maintained throughout the second segment.

So according to FAR 25 within the WAT limits a 2 engine jet is certified to achieve a steady 2,4% climb gradient.

Can you point me too a reference that says it only momentary?

I'm not sure what you are getting at with Far25.111 and 115. First of all 115 simply defines the takeoff flightpath and nett takeoff flightpath.
111 determines another regulatory climb gradient 1,2%.

FAR 121.189:So 189 (a) determines amongst others the certified climb limit weights determind during certification.
And 189 (d) determines obstacle limited weights/climb gradients.

The 0,8% penalty is just for defining the net takeoff flightpath and is used during obstacle climb limit determination. Not performance climb limit determination.

I agree that any obstacles penetrating the 35ft obstacle clearance on a net takeoff path of 1,6% will lead to a higher required net takeoff path and thus gross takeoff path.

But this is a far 121.189 Operator requirement not a far25 certifying requirement like the 2,4% gradient.

In that sense the 1,6% figure is irrelevant, because as operators we need to take the actual obstacles into account and assure that the net path clears them by 35ft.( 121.189 d) We don't do this by starting of at 2,4%. It is done by taking all relevant obstacles into account, add 35 feet, determine the net path. Then add the penalty and thus determine the gross flightpath required. This could be 2%, 3% 5% etc...
For all these percentages you could make a specific WAT table that determines the limiting weight.

If there are no obstacles we are still limited by certifying limits (121.189a) like the 2,4% 2nd segment WAT limit (or required groos obstacle climb gradient is less than the certifying limit)

But this is a far 121.189 Operator requirement not a far25 certifying requirement like the 2,4% gradient.

One needs to keep in mind that second segment WAT is 2.4% and not related to nett. However, whatever gross is required for obstacle or other operational need is then linked to a net capability 0.8% less. Put it down to minor emphasis in meaning.


WAT limits ... a steady 2,4% climb gradient. Can you point me too a reference that says it only momentary?

The physics of the matter is the reference.

As soon at the ambient conditions (Hp/OAT) vary, the steady climb performance will vary ergo the gradient may reduce through the climb. To satisfy yourself on this one, have a look at any WAT chart with different entry arguments.

The reference to steady is to preclude enterprising things, such as a bit of zooming, etc.

Necessary, also, to keep in mind that the regs can't be read in isolation. One needs to review ACs, policy letters and the like to get a story which, itself, varies over the years .. hence one Type will have different rules applied compared to another.

Hi John

I edited my post above. I simply make a clear distinction between what we as operators should do far121.189 and what the certifying manufacturer should do far25.

Off course they are linked, but as long as we stay within AFM limits the aircraft will perform to its certified limits ie. 2nd segment 2,4% WAT. As you said it is not related to net and thus not to obstacles.

For us as pilots the important things are to not bust AFM LIMITS like 2,4% WAT in 2nd segment. And ensure the net takeoff path clears all obstacles by 35ft by ensuring the aircraft is not too heavy to achieve the required gross path.

The mentioned 1,6% over complicates this and is simply not relevant. In fact it is only relevant where obstacles determine that exactly a 1,6% net path is required. But this is determined by obstacles not certifying limits and would be a pure coincidence.

In other words we check what climb gradient is required based on obstacles and AFM limits and take the highest to determine our limited weight.

Time for us to go have a beer, methinks..

Haha I wish... Not for another few hours

737Jock
No.

Pilots don't have the requisite obstacle data to perform those calculations.

Part 25 instructs the manufacturers on the weight limits and performance data that must be provided in AFM's.

In FAA-land, 121.189 is the operating regulation.

AC 120-91 describes how operators can comply with 121.189. It also makes clear that TERPS and OEI operations are not the same.

The calculations are far too complex for pilots who are not performance engineers. :)

The calculations are far too complex for pilots who are not performance engineers

Not really the case .. and the AFM leads one by the hand in any case.

Having detailed and accurate obstacle data is the problem .. which is why pilot calculations generally are based on simplified data appropriate to obstacle clear surface data.

Not really the case .. and the AFM leads one by the hand in any case.

Easy for you to say, jt... :)

Having detailed and accurate obstacle data is the problem .. which is why pilot calculations generally are based on simplified data appropriate to obstacle clear surface data.

Oh, I'd agree that most pilots could find the WAT limits if there were no obstacles in the regulatory departure corridor.

I'm only suggesting that if one gave a reasonably complex departure problem with both close-in and distant obstacles -- one that would introduce thrust time limits and selections of clean-up heights -- to 100 line pilots, it would be surprising if not impossible to find more than five correct answers to the question of "what is the maximum allowable TOW?"

Ok I let something do it for me, it is called a computer. And what I said is exactly what it does.

Btw I'm in jaa/easa-land.

Please help me understand.

Does the "computer" have obstacle data for each runway? If so, how is the obstacle database updated?

Thanks,

Z

a reasonably complex departure problem with both close-in and distant obstacles

Generally, the pilot doesn't have the time to run a detailed calculation during line operations.

The traditional method used in Oz works OK -

(a) the aerodrome owner publishes runway distance and obstacle clear splay data

(b) the operator publishes a simplified set of performance data which is suited to runway distance and obstacle clear gradient calculations. This can be in a variety of presentations but none is too difficult for Government work.

We occasionally used this sort of stuff on the line, generally when a NOTAM or similar temporarily invalidated the normal company RTOW data for a runway. The general caveat is that the technique is restricted to simple straight ahead departures.

Thanks for the explanation, jt. :ok:

Yes it does. The computer is updated every 2 weeks /every month or so. It even gets modified for Notams, and has specified engine out procedures for each runway.

In addition you can add obstacles yourself. Reduce runway length at begin or end, adjust for 90 degree or 180 degree lineup etc etc etc And do multiple runway calculations at the same time. And off course it has all usable intersections for departure listed as well.

Oh and off course you can add all kinds of performance affecting MEL and CDL items.

The laptop is called LPC for airbus (my username is a bit outdated;) and the software FOVE.

It also does W&B landing perf dispatch and inflight and offcourse contaminated runway perf. Again all with MEL/CDL integration.

Thanks, 737Jock.

I had begun to visualize pilots poring over charts, graphs and obstacle data... hence my comment that pilots aren't capable of making the requisite calculations.

My apologies for sound so patronizing; I appreciate your taking the time to describe LPC/FOVE.

Steady climb
 

737Jock,

Can you point me too a reference that says it only momentary?

I think you chose to emphasise the wrong part of the regulation. :=

The point at which the performance must be demonstrated is emphasised, the nature of the performance must be steady and not as a result of any temporary trickery like zooming/speed bleed, ground effect, etc., but there is nothing that says it must have the same value at the end of the path as it did at the beginning. :cool:

Stay Alive,

:ugh: you might want to read john's reply explaining why the 2,4% can vary. This is definitely not the correct answer.

No the configuration in which the performance must be demonstrated is emphasised.

OK... Ill toss a grenade into this campfire...

FAR 23 and 25 are CERTIFICATION standards... The manufacturer (not the pilot) is responsible for certifying the aircraft therefor these regulations are applicable to someone wanting to obtain or change the type design of the aircraft.

Sec. 25.1
Applicability.
(a) This part prescribes airworthiness standards for the issue of type certificates, and changes to those certificates, for transport category airplanes.
(b) Each person who applies under Part 21 [New] for such a certificate or change must show compliance with the applicable requirements in this part.

Part 25 aircraft are not allowed the use of TR's, must have brakes worn to limits, and have an Engine Failure Recognition time built into performance calculations. Does this mean pilots are not allowed to use TRs, should always have worn brakes, and wait 2 seconds after Vef to initiate an abort? Of course not...
Remember that when the FAA determines a new aircraft complies with ALL of Part 25, it is issued a Type Certificate. As long as the aircraft continues to meet requirements of the TC, it complies with Part 25 (among others) and the Airworthiness Certificate is valid. It is not up to the pilots to ensure compliance with 25.903, 33.76 or 25.1455 any more than it is their responsibility to ensure compliance with 25.121. The aircraft met the requirements when it was certified and WAT conditions will not invalidate an Airworthiness Certificate.



Aircraft Certification and Climb requirements
During certification, Part 25 only requires that manufacturers establish weights, altitudes and temperatures (WAT) that produce particular climb gradients (see Part 25.111, 25.115, and 25.121) and publish that data in the AFM (it would require about 5 pages). However, I have hundreds of pages of WAT data for climb gradients ranging from 0.0% 2nd segment OEI to as high as 14% using weights lighter that my BEW (9% is about the most realistic number I can achieve OEI). Why are they publishing such wide ranging data? Because there is no regulatory requirement that an aircraft actually have a 2.4% climb gradient (or any other gradient) under every possible WAT combination when it comes on off the production line (its physically impossible). The minimum legal climb gradients that a pilot will be required to meet will be established by a number of variables ranging from OpSpecs to country of registration.

All US registered aircraft must meet the applicable requirements of Part 91 unless they are subject more stringent regulation. Turbojet aircraft are no exception. An interesting point is that under Part 91, there are no regulations that require climb requirements above 35' be calculated by a pilot (91.605). While WAT were established during aircraft certification that produced particular gradients, the aircraft does not have to be operated at those WATs. As long as there is approved data in the AFM (again, I have data for 0.0% 2nd segment OEI operation) and you do not exceed a published limitation in the AFM, you are legal for a Part 91 flight.



Accept a departure procedure or instrument approach (MACG), operate under 121, 135, 125 or just want to physically climb over anything taller than a lake with OEI and it gets more complicated.. Legal does not mean safe.


SIDS and DPs
I think this was in some earlier posts but if you accept a departure procedure, you are expected to maintain the appropriate climb gradient – all engines operating. Does your acft manufacturer publish all engines operating climb data? Mine does not, so (if yours does, skip ahead) how does one know if they will meet the climb requirements without a AFM data. You don’t….
You will not find anything in the regulations or AFMs that allows you to use OEI data to calculate all engine operating climb gradient. Would your Check Airman let you use a flaps 12 table to calculate a flaps 20 take off?. Of course not...

As logical as the argument may be, it isn’t legal (remember, Safe does not mean Legal).
FYI - There have been some ALJ decisions and FSIM guidance that is slowly changing this but, as of now, this is what we have.


Engine Failure
Lose an engine at V1 and what are you legally required to do under Part 91? Assuming you have decided you have an emergency? Nothing.
Hopefully you have made some calculations with regards to the laws of physics but TERPS, FARs and AFMs do not trump Emergency authority. Climb at 0.0 westbound across the Pacific until you have burned off fuel – that’s legal. Legal does not mean safe.



That should be enough dynamite in the campfire for one night.. I welcome your input and the references that go with it.

Skky, If you believe you can legally operate at less than the certified limits simply because data outside those limits is included in your AFM I'm afraid you are mistaken.



Not so much a grenade as a big fat cream pie.

The Airworthiness Certificate states that the airplane must be operated in accordance with the Limitations stated in the Airplane Flight Manual. These limitations include structural limits (MTOW, MLW, MZFW), CG limits, max operating speeds, and WAT limits.

I was told by a captain that the FMC of the aircraft (B737) calculates the performance of the aircraft on the SID for one engine out event when you enter the SID. Can someone confirm this? I was not able to find any reference to support this statement so I am not sure if this is correct.

If I might emphasise the comments of intervening posters ..


It is not up to the pilots to ensure compliance with 25.903, 33.76 or 25.1455 any more than it is their responsibility to ensure compliance with 25.121. The aircraft met the requirements when it was certified and WAT conditions will not invalidate an Airworthiness Certificate.

Of course not .. however, it IS up to the pilot to ensure that the aeroplane is operated in a manner which is not inconsistent with the Standards embodied in the design (eg Part 25).


The minimum legal climb gradients that a pilot will be required to meet will be established by a number of variables ranging from OpSpecs to country of registration.

.. and that will be the page in the AFM which details the WAT limits.


As long as there is approved data in the AFM (again, I have data for 0.0% 2nd segment OEI operation) and you do not exceed a published limitation in the AFM, you are legal for a Part 91 flight.

That may be the case (my bolding, above) but there will be another chart which gives the WAT limits .. the how-to-use-it data will indicate that the WAT limit comes first then the other stuff ie, if the second segment charts have data apparently below the WAT limit, that will be for interpolation or similar reasons ..


Climb at 0.0 westbound across the Pacific until you have burned off fuel – that’s legal

That would be constrained by operating rules rather than design rules. However, why would one wish to do that when the aircraft should be quite capable of climbing as per the normal segmented flight path (I presume we are talking heavies) ?


I was told by a captain that the FMC ..

No reason why one couldn't set up such an animal. The sums are fine for the least capable PC .. However, the database amendment workload would escalate dramatically.

I suggest that a more reasonable expectation (unless you have documented evidence to the contrary ..) is that the box will tell you what you can expect to see OEI depending on the weight, Hp, OAT it thinks exists .. but with NIL consideration of any specific terrain .. including SIDs.

to add to JT's post..

There is nothing in the design criteria that addresses EO. It is considered an emergency op. Nothing in charts(unless you had them privately designed) will reference EO.

That is not true. There are no EO DP procedures unless you had one customed designed.

You will find that for twins, if you actually calc it out, that there is virtually no way you can meet SID requirements EO, or missed EO in gradient, unless you have a special procedure designed, or limit your weights.

if you are EO, you dont have a level off 2nd segment.

Again, nothing in procedure design criteria references EO, either in missed or departure.

FPO

For some strange, inexplicable reason, I think he is referring a second segment "climb" of 0.0%, that is zero climb.

GF

@FE Hoppy – I’m not sure I understand what you asked/stated but if you are not limited by the AFM or regulation, then it is legal. Data will not be in the AFM unless it is approved during the type certification process which is done in compliance with Part 23/25.

(*AFMs may actually have unapproved data but it must be clearly notated. For example, I have overweight landing Vref speeds but that does not authorize me to plan overweight landings.)

@HazelNutz39 – there is no requirement in Part 25 that a manufacturer provide operational data that exceeds any particular climb gradient. Certification rules (Part 25) say that the manufacturer will provide each WAT within the operational limits of the aircraft that produce a climb gradient of 2.4% OEI (two engine acft). In other words, it’s not contrary to Part 25 for manufacturers to publish a WAT for a 0.4% second segment OEI climb, nor is it contrary to provide data for a 14% second segment OEI climb.
I completely agree, you must comply with what is in the AFM (FAR 91.9) and MTOW, altitude limitations, temp limits (min and max), CG limits, Vne ect. Remember that performance charts are the laws of physics – simplified. If you configure an aircraft as per any performance chart, the aircraft CANT do anything else but deliver the numbers in the book.
As for 91.605, I agree you cant depart an airport that you don’t have performance data for (or is prohibited by the AFM), but Part 91 does not specify climb gradients after 35’. I other words, I am in compliance (legal), if I have a WAT in my AFM for 0.4% OEI climb, and I can legally depart. Consider the implications of 25.117.


@john_tullamarine I agree, the AFM is created for the sole purpose of ensuring that the design limitations are clearly outlined. FAR 91.9 then elevates the guidance in the AFM to that equal to a regulation. There will not be anything in an AFM that is contrary to a certification regulation (the FAA will not approve it).
AFMs do not specifically require a minimum climb gradient. Every AFM will have the data required by FAR25.121 and most will have more data but no AFM will have less. If you need a particular OEI gradient, the performance section will tell you what WAT will give you your requested climb performance. The OEI climb performance you require may be due to TERPS, OpSpecs, 121/135 regulation, DP, noise or JAA/CAA. If in the course of trying to obtain the desired climb performance, you “run off the chart” or data is not provided for your desired OEI climb then, yes, you must find another way. You are allowed to interpolate but cannot extrapolate.
I am interested as to what the lowest OEI climb gradient is published in your AFM. MGTOW, 40C and 4200 msl will result in 0.0% OEI climb in mine.


@FlightPathOBN – FAR 23 and 25 are aircraft design certification requirements and FAR 25.121 is titled Climb: One- Engine Inoperative. All most all of my climb charts are OEI (in fact all engine operating charts are the issue). There are several companies out there specializing in custom departure procedures (and they are affordable). We reference them for 90% of our take offs and brief the alternate departure procedures in about 25% of our operations. We meet the SID climbs with OEI the rest of the time. As for MACG, we don’t often calculate that (but we should) and we have procedures to adjust our mins so that we can meet a MACG in places where it becomes critical (ASE in the summer for example).

The plane MUST be operated within its certification rules which includes the WAT limit of 2.4% climb gradient to a minimum of 400' AFE. You cannot blow off the certification standards by saying you are FAR 91.

GF

Skky,

hmmmm...my favorite to use is a company called Operations Based Navigation!

There are only a few airlines which have OEI procedures in the FMC, and they have been associated with RNP procedure designs. There is one for Burbank, so they didnt have to limit weights on hot days...
and I am glad that you realize that SID, or the missed approach on a plate is not OEI.
I mean you could use them, as long as you calc out OEI performance with temp, and unload the aircraft!

what are we talking about here?
 

Skyy,

Are you talking about private operations in something like a Global Express? :confused:

Stay Alive,

@4dogs – Yes.. Part 91 operations in a jet aircraft


@FlightPlathOBN – I use Aircraft Performance Group Welcome to Aircraft Performance Group They can do runway perf for any airport (they haven’t failed me yet).. they just need your aircraft loaded into their database. They often use the same flight path as the published Departure Procedure but because their lateral clearance is less than TERPS, you can depart heavier (that will start another conversation I'm sure). The advantage is you already have it in your FMS. When they provide a completely new procedure, it is not too difficult to plan/program into an FMS. We have company procedures that outline how this is done.
Its not so much of a “realization” as it is just reading it. TERPS says quite clearly that it is not OEI. Furthermore OEI is an Emergency (at least in my book) and continuing on a DP and trying to meet a climb requirement when there is a perfectly viable escape route available is – in my book – the very definition of careless and reckless.
You are exactly right, about offloading… If I may paraphrase the whole thing, you essentially need a “Plan B” to be legal. Plan B may be an escape procedure, it may be flying the DP at a weight that allows you to meet the climb requirements OEI, or it may be fly over the ocean until you can climb high enough to turn around. As long as you can prove your “Plan B” is viable (and you can climb to 35’), you are legal. Many operators choose to offload in order to comply with the DP OEI. Nothing wrong with that – other than you may not have actually been required to do that (again, from a purely legal perspective). (and I’m sure you meant Landing Climb).


@galaxy flyer – can you show me where in the regulations (Part 91 operation) where it says a pilot must operate an aircraft with a 2.4% to 400”? Psalm and verse if you please.


Thanks

Correct, except that the climb gradient of 2.4% is for the "thrust available at the time the landing gear is fully retracted". Since thrust reduces with altitude, the gradient at 400' is usually somewhat less than 2.4%. The WAT limit requirements of 25.121 are related to, but also distinct from the takeoff path requirements of 25.111.

Skky is probably a 'troll' who knows perfectly well that it's illegal to operate an airplane outside its operating limitations.

herewith is your psalm and verse.... FAR 25.121 Airworthiness

Mutt

You also have to comply with ICAO annex 6, part 2, chapter 5, as the USA didn't file any differences.

Mutt

Mutt:

In the U.S. that transfers to the applicable commercial flight operations regulations. But, for the non-commercial operator flying a Part 25 aircraft it does not. Part 91 does require the non-commercial operator to calculate the balanced field for takeoff but once airborne there is no specific requirement to make good the Part 25 takeoff flight path, all engines operating or OEI. With all engines operating he is bound, though, by a SID climb gradient as I would be in my Part 23 bugsmasher.

Skky,

Thanks for the link. Interesting app. for the smaller ac...

Ok, skyy, your point might be true, BUT why would any responsible operator of Part 25 aircraft NOT try to achieve the highest standards by using appropriate runway analysis for departure? We, and a number of operators, use APG or equal on all departures.

GF

Part 91 requires you to operate in accordance with the flight manual limitations.

Below is a typical AFM from a Part 25 a/c.

2. MAXIMUM ALLOWABLE TAKE-OFF WEIGHT
The maximum allowable take-off weight is limited by the most restrictive of the following:
• Maximum approved take-off weight
(Refer to Chapter 2; LIMITATIONS – STRUCTURAL WEIGHT),
• Runway length available,
• Climb requirements,
• Obstacle clearance requirements,
(First, verify if the second segment of the take−off flight path extends beyond a pressure
height of 1,500 feet above the airport and consider if potential adjustments are to be made.)
• Maximum demonstrated brake energy,
• Maximum tire speed,
• Wheel brake cooling limitations
(Refer to PERFORMANCE – TURN-AROUND TIME – Cooling of Wheels, Brakes and Tires,
in this chapter).

Note that obstacles are in there as well.

It seems pretty unequivocal to me - which bit of Maximum Allowable Takeoff Weight do people have a problem with? :ugh:


Apart from the legal considerations, why would anyone not want to take the climb performance into account? A 2.4% gradient with no obstacles or 35 feet clearance if there is seems pretty sphincter tightening to me:sad:

Added to which, in my book I'm being paid to keep the boss safe - and he thinks so too. He would probably be mightily unimpressed (= me fired) if he though I was gambling with his and his family's safety.