2.4% regulatory climb gradient for single engine
 

I read in one of the posts that multi-engine plane must meet regulatory climb gradient for single engine of 2,4% in order to takeoff. If my single engine performance is less then 2.4% am I not allowed to depart ??? Could someone please elaborate on it.

That is true.

Maybe... See FAR 25.121(b) for one set of regulations. Where are you, at what point are you measuring, and in what configuration?

I'm guessing that you're referring to second segment performance...what about obstacle clearance or runway geometry limits?:hmm:

The required gradient varies with number of engines. That is the minimum gradient to meet certification rules and applies even if departing over a cliff and the flight path is over the ocean w/o and obstacle in a thousand miles.

GF

GF:

It's important to note that the operating rules (U.S. 121.189) require that the certification takeoff flight path (Part 25) be increased as necessary to avoid any obstacle that penetrates the certification surface and cannot be avoided laterally.

Also, there are the gross and net paths.

Aterpster

No argument there, just posting the certification case. Obstacle clearance is also required, in all cases, not just when a obstacle gradient is published. i.e. 3.3% minimum.

GF

Your runway analysis or performance calculation considers many variables any one of which on a given day on a given runway could be the limiting factor for your t/o. The climb limit is all about your engine out climb capabiltiy. On a twin you are meant to achieve a 2.4% gross or 1.6% net gradient. (numbers are different for 3 & 4 eng. a/c.) The .8 % difference could be the air between you and the rocks if you are climb limited.

SID's are based on a 3.3% climb gradient which is why flying a SID with an engine out is very brave unless your company has assessed the SID to assure that 2.4% will keep you safe. There are companies that do this to simplify their performance calculations, which is fine for them but it muddies the waters for the rest of us as their pilots then will insist that flying the SID with an engine out is safe. It may be for them in their specific op. but it's generally not.

J. T. We need your quiet voice of reason on this.

Aterpster, what do you consider to be the certification takeoff flight path, do you consider it to end at 1500 feet (Note, I know that he is in FAA land :))

Dariuszw How do you account for obstacles in the CitationJet??

Mutt

My obsticle avoidance is accounted by following sids which is official single engine out procedure and no Mutt, Im definitely not in FAA land anymore :( at least not for the last four years. Im in JAA's land now. Anyway, thank you for your answers.

Some comments -

If my single engine performance is less then 2.4% am I not allowed to depart

Correct with caveats.

If your OEI (presuming you are talking a twin) gradient capability is less than 2.4% (gross) for second segment, then you are above the AFM WAT limit for the conditions and considering operating outside the AFM certification limits.

WAT limits are the limiting gradient requirement to provide some modest climb capability regardless of any other consideration.

unless your company has assessed the SID to assure that 2.4% will keep you safe.

.. or, more likely, has restricted RTOW to provide a profile appropriate to the SID.

but it's generally not

fair comment

This is true and I have been turned away for this very reason.

WHAT??????

Can you please supply a reference for this statement, start with your Jeppesen Manual.........

Aterpster is in FAA land...... :)

Mutt

The aircraft is certified at 2.4% for the 2nd segment. Within its flight envelope it will always make this. This is simple regulations. And you cannot depart outside the aircraft limitations (to which the aircraft was certified) under any normal circumstances.
So the only thing that can be done is finding more performance (new certification), reducing weight or finding a regulator that will allow you to operate outside AFM limits.

The gross flightpath is simply the takeoff flight path that is ACTUALLY flown by the aircraft (starting 35ft above the end of the takeoff distance)

The net flightpath is the gross flightpath minus a mandatory reduction of 0.8% (twin)
The net flightpath ALSO has to clear all obstacles by at least 35ft

The climb limit therefore only arises when the gross flight path minus 0,8% (net flight path) does not clear all obstacles by at least 35ft.

The 0,8% is therefore an extra safety margin (I guess for mishandling) on top of the minimum obstacle clearance of 35ft. It is not the obstacle clearance itself.

Mutt;

In the abstract of Part 25, I believe it does end at 1,500.

In the real world of 121.189 it ends at 1,500 only if en route climb can be achieved at that point ( 5 s.m. each side of centerline and in en route climb configuration).

Unlike you I am not a performance engineer. :ooh:

Maximum Weight Permitted by Climb chart
 

Does any one know what the "Maximum Takeoff Weight Permitted by Climb Requirements" chart uses for a minumum gradient? I assume this is a single engine chart.

Mutt:

Mutt, the regulation was changed a couple of years ago to encourage commercial operators to overlay their OEI performance calculations first on the airport's basic obstacle departure procedure ("ODP," used only at light traffic airports) or the applicable SID provided the SID can contain the Part 25 flight path, but using AC 91-121 splays rather than the TERPs splays that were used to design the SID. In such case the SID is the preferred flight path for OEI. Of course, if this assessment of the SID passes OEI muster, then the SID will be so designated by the operator.

In many cases the SID won't work, in which case the game remains unchanged, with one exception. If transition from the SID to a feasible OEI path will not work when an engine fails after takeoff but early in the departure phase the operator is permitted to develop its own departure procedure that will work for both normal (comply with TERPS) and OEI conditions(AC 90-121). This option is not used often and then only when ATC will accept it in advance (usually at lighter traffic airports).

The maximum TOW limited by climb requirements (WAT limit) for Transport Category Airplanes is based on the most limiting of three T.O. climb requirements with one engine inoperative (gradients for twins):
25.121(a): 0%; Vlof; gear down; T.O. flap, T.O. thrust
25.121(b): 2.4%, V2; gear up; T.O. flap; T.O. thrust
25.121(c): 1.2%; Vfto; gear up; flaps up; M.Cont. thrust

The conditions for these requirements differ in some details from those used to establish the take-off flight path, notably with respect to the variation of thrust with altitude.

That is not correct. The WAT limits are a certificate limitation and apply regardless of obstacle clearance considerations for all types of operations. Obstacle clearance by the Net TOFP is required by operating regulations such as FAR 121 for Air Carriers.

Dariuszw:

Do you have an authoritative cite that all SIDs in JAA-land are OEI compliant?

Of course he doesnt...:suspect:

Would be hard to follow an SID with 8% or higher required initial gradient with an engine inoperative.

But then in days gone by we had a pretty conservative performance manual. Standard procedure was to follow the SID and the performance took that into account, only if not possible was there an EOSID on the WAT chart of the runway. Nowadays we would never follow the SID, if no obstacles present (well, obstacles we have to consider) we just fly straight out for the next 30NM by which time we should be above the required minimum altitude.

in days gone by we had a pretty conservative performance manual. Standard procedure was to follow the SID and the performance took that into account

although, presumably, making a profit was not high on the list of priorities ?

we just fly straight out for the next 30NM

in many places that approach imposes a high workload on the ops engineering cell when there may be much simpler general escape techniques available.

Also, the DP may be predicated on noise abatement primarily , resulting in severe weight penalties, when a more economical NTOFP can be constructed that allows greater weight to be carried...As J_T mentions above

:)

FYI: 737 Jock got it right.

Maximum Takeoff Weight Pounds Permitted by Climb
 

I found my own answer with Cessna. This is a certification chart that guarantees you can do at least a 1.2% climb gradient on TWO ENGINES for a Part 25 aircraft.

WTF? 1.2% gradient? You are kidding, correct?

GF

Just to be clear- Part 25 aircraft are certified and required to be operated such that they will climb the certified amount of gradient under one engine power, under all conditions. To consider only climb gradients for IFR departures and SIDs is folly...a plane that will not fly single engine on a sunny day, is merely being able to see ahead to the scene of the accident.

Another avatar

Have you heard of 3 and 4 engined planes? Presumably, they will not fly far on a single engine.

GF

GF:

Well, three engine birds will if managed properly. I flew two different types for much of my career; 727 and 1011.

The 1011 was an international bird, it had to make with to a landing at an airport after loss of two engines at the ETP. I think the level-off altitude would have been fairly low although I never tried it.:)

Further, every simulator session had an outboard engine fail just above V1 at MGTOW, then as soon as cleaned up and starting en route climb the center engine would always fail. Flew around then dumping fuel to max landing weight followed by a single-engine ILS to landing.

SID departure climb gradient requirements and engine out climb requirements are two totally different requirements.

Engine out requirements certification - Part 25 certification requires different mandatory minimum climb gradients based on segment and number of engines. Example. Part 25 requires that a 2 engine aircraft be able to attain 2.4% gross climb gradient during the second segment climb (gear up to a minimum of 400agl). Second segment climb requirement is in most cases the most restrictive and that is why that number is most commonly used. Also, some aircraft manufactures will extend their second segment to 1500 agl

FAA regulations. FAR s part 121 & 135 now decide how we clear obstacles using the above certification. First, they build in a safety margin by using a lesser climb gradient. For a 2 engine aircraft they use .8% less for a total of 1.6%. This is known as net climb gradient and accounts for the fact the pilot will not perfectly fly the aircraft OEI like during certification. They then say that during all segments a pilot must clear all obstacles in the departure corridor by 35ft. Departure corridor extends laterally 200 ft in airport boundaries and 300 ft from wingtip outside airport boundaries. Once again 2nd segment is usually most restrictive so that is why we usually talk about second segment net climb gradient clearing all obstacles by 35 ft

SID departure climb gradients. One important thing to know is that SID climb gradients are based on aircraft operating normally (all engines operating). Also their climb gradient 200 ft/nm or 3.3 % is a linear climb gradient and not segmented like on part 25 certification and how we actually fly the engine out departure.

Engine out is an emergency procedure and therefore allows us to not not follow the SID. This is where alternate engine out departure created by an airline or 3rd party company are allowed, legal, safe and often used to increase max takeoff weight

Well, three engine birds will if managed properly

Depending on the jurisdiction, if the 3-/4-motor aircraft doesn't have data for two out, it may/will be restricted to 90 minutes. So, for instance, IPEC with their Argosy fleet in Oz had a 90 minute restriction - as I recall, they came up with an AFM change to address that original deficiency.

every simulator session had an outboard engine fail just above V1 at MGTOW, then as soon as cleaned up and starting en route climb the center engine would always fail

AN did the same for the L188 on base checks as the airline didn't have a sim for the Type .. performance on two wasn't overly enthusiastic. Indeed the second failure occurred during second segment once there was enough height for the subsequent descent and reconfiguration.

Similar for the B727 .. never comfortable with the second failure and getting down quite low whilst clawing one's way to (as I recall) 200kt ?

during all segments a pilot must clear all obstacles in the departure corridor by 35ft.

Minor caveat .. 50ft during turns to account for the wing down pod on a four engine bird.

Aterpster

I take your correction; I did some time in the Boeing Tri-motor. It just seemed that the previous poster was too twin -engine oriented the way it was phrased.

GF

As a minor point of interest...second segment isn't always the most restrictive as mentioned above. An example is the ATR with an engne out in icing conditions where the flaps remain at the takeoff position until a higher speed is achieved compared to non-icing conditions, resulting in the 4th segment being most restrictive.

J.T.

As OK465 states, we never lost the second engine until clean, and at least 200 knots.

I can't imagine losing the second engine while still dirty and not buying Farmer Jone's farm.:)

we never lost the second engine until clean, and at least 200 knots

How fortunate .. our deal saw the second one go during the second segment (too long ago to recall actual specifics) .. F/E started dumping like his life depended on it .. nose down, accelerating while the flaps were coming up. Bottomed out around 200 kts as the flaps finished running and then a modest climb.

No-one ever had any major problem in the sim with the exercise.

However, not something to contemplate with a nasty aerodrome.

It is correct, as long as you are within WAT limits and there are no obstacles to consider you are not climb limited! Or are you suggesting that it is allowable to takeoff outside WAT limits?

Which is what I said, as long as the gross flightpath minus 0.8% (=net flightpath) clears all obstacles by 35ft. If it doesn't you will be restricted by a 2nd segment climb (since we are discussing the 2,4% requirement) limited weight. Thus you will be climb limited.

737Jock;
We agree on the substance but are using different terminology. What you call "climb limited" would be "obstacle limited" in my terminology. My apologies for the misunderstanding.

It is correct, as long as you are within WAT limits and there are no obstacles to consider you are not climb limited!

What HazelNuts39 said regarding obstacle limited. The general terminology use is to refer to "climb limited" when citing WAT limited.

Which is what I said, as long as the gross flightpath minus 0.8% (=net flightpath) clears all obstacles by 35ft. If it doesn't you will be restricted by a 2nd segment climb (since we are discussing the 2,4% requirement) limited weight. Thus you will be climb limited.

With respect, good sir, I think you should have a review of the Design and Operating Standards. The 2.4% has naught to do with obstacles and applies as an AFM maximum weight where, and if, limiting.

Because we f;ew the 727 into so many caribean airports with few obstacles but a lot of birds, I asked our check airman to fail two engines at 500 ft on takeoff after we had completed our sim checks and had some time left. I wanted to see if it was possible to clean up before hitting the water since we had no training procedure for that. He initially told me I had to be at 200 knots but he would do it if I wanted to try it.

We got down to 300 feet before we had 200 knots and could climb again but made it by retracting flaps slightly early and using a shallow descent. I thought we might need to get into ground effect to accelerate but we never got that low. We started at V2+10 as in our normal climbs. It gave me confidence that I may not be commited to ditching if it ever happened. If it wasn't working I could still go back to a higher flap setting if ditching was required. Our engineer had to leave so we couldn't dump fuel.

Someone told me Fed Ex trained for this.

Got to disagree with you, if you cannot achieve the required certification climb gradients you are climb limited, if you cannot clear obstacles in the takeoff flight path then you are obstacle limited.

Regardless of the nomenclature on your takeoff charts, these are the limitations. To test it, pick an airport with no obstacles and a long runway, then increase the airport elevation and temperatures until you start to see restricted takeoff weights less than the structural, what do you call these weights? Mr Boeing calls them CLIMB LIMIT weights.

Mutt