2.4% regulatory climb gradient for single engine
Thread Starter
Joined: Dec 2011
Posts: 52
Likes: 0
From: Paris, London and New York
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.
Joined: Dec 2002
Aviation Qualifications: ATP+Mil
Posts: 3,983
Likes: 567
From: Where the Quaboag River flows, USA
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
Guest
Joined: Apr 2009
Posts: 3,336
Likes: 0
From: On the Beach
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.
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.
Also, there are the gross and net paths.
Joined: Dec 2002
Aviation Qualifications: ATP+Mil
Posts: 3,983
Likes: 567
From: Where the Quaboag River flows, USA
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
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
Joined: Aug 2007
Posts: 149
Likes: 1
From: canada
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.
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.
Joined: Sep 1999
Posts: 5,552
Likes: 25
From: ME
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
)Dariuszw How do you account for obstacles in the CitationJet??
Mutt
Thread Starter
Joined: Dec 2011
Posts: 52
Likes: 0
From: Paris, London and New York
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.
at least not for the last four years. Im in JAA's land now. Anyway, thank you for your answers.
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,442
Likes: 307
From: various places .....
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
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
Joined: Sep 1999
Posts: 5,552
Likes: 25
From: ME
My obsticle avoidance is accounted by following sids which is official single engine out procedure
Can you please supply a reference for this statement, start with your Jeppesen Manual.........
Aterpster is in FAA land......
Mutt
Joined: Jan 2008
Posts: 3,753
Likes: 0
From: ...
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.
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.
Guest
Joined: Apr 2009
Posts: 3,336
Likes: 0
From: On the Beach
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.
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 
)
)
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.
Guest
Joined: Apr 2009
Posts: 3,336
Likes: 0
From: On the Beach
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).
Can you please supply a reference for this statement, start with your Jeppesen Manual.........
Aterpster is in FAA land......
Aterpster is in FAA land......
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).
Joined: Jul 2009
Posts: 1,682
Likes: 0
From: France - mostly
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.
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.
Originally Posted by Jock737
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.
Last edited by HazelNuts39; 19th February 2012 at 14:06.
Guest
Joined: Apr 2009
Posts: 3,336
Likes: 0
From: On the Beach
Dariuszw:
Do you have an authoritative cite that all SIDs in JAA-land are OEI compliant?
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.
