Climb Gradient for GA

[JPAirbus]

As far as I know, we do have different requirements on GA Climb Gradients:

1. Certification requirements:
   CS25/FAR25:
   Landing Climb Gradient of 3,2% (All Engine; LDG Configuration) - not limiting on most jets.
   Approach Climb Gradient of 2,1% (2 ENG), 2,4% (3 ENG), 2,7% (4 ENG) (OEI; Appr. Config - i.e. Gear Up) - might be limiting
2. Procedure Design Requirements:
   PANS OPS / ICAO Doc 8168 2,5% (All ENG)
   TERPS / FAA Order 8260.3D:
   It states in "2-8 -5. Straight Missed Approach Obstacle Clearance." that a 40:1 surface should not be penetrated, which leads to 2,5% (regardless of configuration and engine availability).
   It states in "2-1-4.Sloping OCS." under point "b.Climbing on departure or missed approach." the following: "(...) The minimum climb gradient that will provide adequate ROC in the climb segment is 200 ft/nautical mile (NM), unless a higher gradient is specified." Those 200ft/NM would lead to a 3.3% gradient.

The above mentioned TERPS excerpts call for either 2.5% or 3.3%. My company tells me, that within the TERPS Area (US and CAN) the required gradient for GA (OEI and All ENG) will be increased to 3,3%.
What are the requirements? Do we need 3.3%, or do we need 2.5%?
I appreciate any hint!

[eckhard]

1. These are aircraft performance requirements, a bit like the take-off climb (WAT) limits; they are independent of location.

2. I think these are procedure design requirements. Perhaps the "40:1 surface" means that for a straight missed approach to be published, there should be no obstacles penetrating that surface? If there are, then a turning missed approach should be designed?

The manufacturer has to ensure compliance with 1.
The aerodrome operator has to ensure compliance with 2.
The aircraft operator/commander has to check compliance and performance compatibility with both requirements, on the day, at the location.

[JPAirbus]

That's the point. Do I check for a GA gradient of 2.5%, or do I have to check for a GA gradient of 3.3%.

[eckhard]

I think that for SIDs, the 3.3% figure has been a requirement for quite some time. If conditions don't allow your aircraft to achieve this with OEI, the operator will have to design a special procedure to be followed. This can be referred to as a "Tailored Departure Procedure", "Emergency Turn", "Engine Failure Procedure", or similar.

For the Missed Approach, I agree that there seem to be two different figures. Bear in mind that the MAP will commence at the runway threshold or earlier, whereas the SID commences at the other end, so you will have some "extra margin" built in for the missed approach performance if you're comparing one with the other, particularly on a long runway.

I guess the safest option is to assume that you will need 3.3% for the missed approach, unless a performance specialist can do a more detailed analysis for you.

[Matey]

Under PANS-OPS the standard Procedure Design Gradient for a missed approach is 2.5%. Approach chart minima are published based on that. If a higher gradient can be achieved then the approach chart can show lower minima based on a higher gradient such as 5%. From memory, an example would be the Runway 01R ILS minima at Dalaman in Turkey (LTBS) which give minima of around 850 feet for 2.5% missed approach gradient and 210 feet for 5% as you can start the missed approach from closer to obstacles with the better gradient.

For Departures under PANS OPS the “standard “ initial Procedure Design Gradient is also 2.5% above the Obstacle Identification Surface (OIS) which is then increased by 0.8% to give 3.3%. Should a higher gradient be required to achieve obstacle clearance then this too is published on the Departure chart with a required gradient to an altitude. Again Dalaman is a good example where the BENEM 1R SID is annotated as requiring a 5% gradient until 7500 feet again from memory. (I retired 4 years ago!) DOC 8168 Vol 1 refers.

[eckhard]

Thanks Matey; good references.

[olster]

Yes 2.5 pc for go arounds normally.

[eckhard]

So, it seems that the 3.3% is the gross gradient required, resulting in 2.5% net. Makes sense.

[Matey]

Just out of interest the type I flew prior to retirement was the 737-800 with 27k engines. This is capable of achieving a missed approach climb gradient of 2.9% on one engine at max take off weight (78 tonnes) at a sea level airfield and +30 degrees C. At max landing weight [65 tonnes) it can achieve 5% at a 1000 foot pressure altitude airfield and +30 degrees. Both from flap 40 approaches. Using flap 30 for approach, and thus a slightly higher speed for the approach and go around, gives a better gradient as does using bleeds off. Thus under most circumstances the lower minima at somewhere like Dalaman could be used at up to max landing weight at least in my usual sphere of operations. And, of course, we always went to Dalaman in the middle of the night with slightly more moderate temperatures!

[JPAirbus]

Thanks guys for the answers!
What I am confused about is the FAA world. Obviously the FAA requires a 3.3% gradient for the missed approach since a short while ago. However I cannot find a clear reference in FAA books about the climb gradients required for missed approach - instead I find the 2 contradicting references I posted below? Anybody wiser than me on that topic?