KC10 FATboy

I'd like to have a discussion with the prior military guys who are also smart on Part 121/135 requirements. In another APC thread, there was a discussion about minimum climb gradients.

The USAF says that we must be able to depart a field one-engine inoperative (OEI) at 200'/NM 3.3% or as published higher unless a Special Departure Procedure (SDP) is available.

Back in 2006, the FAA published an advisory circular (AC) AC 120-91 which elaborated the difference between TERPs requirements [all-engines operating (AEO)] and engine out requirements. The following is from the AC. It states:

7. A. Standard Instrument Departures (SID) or Departure Procedures (DP) based on TERPS or ICAO Procedures for Air Navigation Services—Aircraft Operations (PANS-OPS) are based on normal (all engines operating) operations. Thus, one-engine-inoperative obstacle clearance requirements and the all-engines-operating TERPS requirements are independent, and one-engine-inoperative procedures do not need to meet TERPS requirements. Further, compliance with TERPS all-engines-operating climb gradient requirements does not necessarily assure that one-engine-inoperative obstacle clearance requirements are met. TERPS typically use specified all-engines-operating climb gradients to an altitude, rather than certificated one-engine-inoperative airplane performance. TERPS typically assume a climb gradient of 200 feet per nautical mile (NM) unless a greater gradient is specified. For the purposes of analyzing performance on procedures developed under TERPS or PANS-OPS, it is understood that any gradient requirement, specified or unspecified, will be treated as a plane which must not be penetrated from above until reaching the stated height, rather than as a gradient which must be exceeded at all points in the path. Operators must comply with 14 CFR requirements for the development of takeoff performance data and procedures. There are differences between TERPS and one-engine-inoperative criteria, including the lateral and vertical obstacle clearance requirements. An engine failure during takeoff is a non-normal condition, and therefore takes precedence over noise abatement, air traffic, SIDs, DPs, and other normal operating considerations.

So, am I to believe that the USAF is not compliant with OEI requirements as stated by the FAA/ICAO/PANSOPS?

In relation to the first bolded text above, the USAF does not consider TERPs and OEI requirements independent. In the second bolded statement, the AC says literally that using TERPs requirements during an OEI scenario may not meet OEI obstacle clearance requirements.

Now, the USAF isn't exactly hitting obstacles out there during OEI situations. In fact, has it ever happened?

So my question to the forum is, what is this AC getting at? Why does departing OEI at the TERPs required climb gradient not meet OEI requirements? Is it the horizontal obstacle clearance requirements that aren't being met?

I'm confused and trying to grasp this. If there's anyone out there that's smart on this, I would definitely like to hear from you.

LINKS:

FAA AC 120-91 http://rgl.faa.gov/Regulatory_and_Gu...E/AC120-91.pdf
FAA Video on TERPs, AC 120-91, and their interpretation (fast foward to 12:00)
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Thanks ...

Fatboy

liftr92

I'm no AIS guy, but I found that if I rotate 4 knots prior to tire limit speed or 1,000' remaining, I have enough energy/smash to wifferdill if I hear a "Whoop Whoop pull up". So far this has worked out fine.

fsuskypilot

FATboy,

So if you are down to using the third option, the only acceptable technique to calculate required OEI CG is to subtract .8% (48 ft/nm) from the published CG. This is regardless of whether the published CG was calculated using the old 48 ft/nm required obstacle clearance (ROC) or the current 24% ROC. (fully detailed in 11-217V1 chpt 9)

So with a standard climb of 3.3% (200 ft/nm) your OEI climb requirement is 2.5% (152 ft/nm)

MoosePileit

I'd say it's an AIS question and I'm not a grad-jit... or maybe the reps at Jeppesen (since your airframe uses SDPs also) have an easy way to explain the difference between the advisory circular/FARs and how at least AMC handles climbouts and gradients both all engine and OEI. If your home 'drome has TERPs folks they might also answer that one for you.

When the approach plate or DP says "USAF" on the top and not FAA or USA (Army) I don't know that the "TERPS" done by the USAF is similar enough to the FAA TERPS that this is an apples to apples issue in any way.

KC10 FATboy

I fully understand what the USAF allows and requires us to do.

The big question I have is, the FAA saying that TERPs IS NOT to be used for OEI analysis. That creates a lot of WTFs for me. We've all flown FAA TERPs departure procedures ... and used those published climb graidients to calculate OEI TOLD. So the question I have is, why? What is wrong with the 200'/NM and why isn't it always good? Additionally, why doesn't USAF TOLD take into account the horizontal separation requirements?

SDPs, when they came out, were a vast improvement over the way we used to do TOLD (KC-10 guys can definitely relate). But SDPs initially were designed to get you 35 feet above the obstacles (not sure about the horizontal). But the USAF in their infinite wisdom decided to reduce this down to 0 feet ... as normally required. I think this was a big mistake. But then again, we've not hit anything so who cares?

I hear the SDPs aren't very popular up at HQAMC / HQUSAF ... and they intend to make them go away. BIG mistake -- especally after reading the Advisory Circular. Something just doesn't jive.

MoosePileit

Not to argue- but how can you NOT like an SDP? (That's for mother MAC, not you KC-10 FB).. It lets me carry the max cargo with the minimum amount of work. It's win, win for AMC. I used to run a demo on the C-17 showing how you'd save a bunch of prep time and get more cargo on board using the SDP. I don't mind making my own departure weights- but the customer and mother MAC may not be as happy.

Will the IFM folks become real by the FAA book of definitions, "dispatchers" and tell us our cargo and departure weights? Tcha.

Till then, give me the SDP. Even then "they" miss the icing conditions and wet runways that can cut into their planned payload.

ALWAYS, unfortunately, a GREAT topic.

LivingInMEM

I don't believe the FAA is saying that TERPS is NOT TO BE USED for OEI. What it is saying is that is does not have to be, and is usually not by many aircraft performance charts.

Running your all-engine data for an FAA certified aircraft does not automatically give you obstacle clearance in the event of a loss of one engine. If your OEI performance still guarantees the required climb performance, you are golden. For many operators, we run all engine performance then reference a special engine out departure procedure that gives us a obstacle cleared flight path to follow in the event of an engine failure. If our data was for engine-out, we would not have to reference that page.

KC10 FATboy

I agree Moose 100%. For years, the KC-10 operated knowing we would go below the 2.5% plane in the event of an engine failure. Then we got Change 7 to the 1-1 and that moved the entire OEI profile above the 2.5% plane. The result, grossweights were reduced. Then came SDPs. I like them very much for the same reasons you do. Carriers are responsible for their own OEI obstacle clearance requirements so they publish the same thing (called Engine Out Procedures (EOPs) by the FAA) which is what LivinginMem was referring to. This Advisory Circular dictates the two methods at which those EOPs can be created.

LivinginMem, I don't necessarily disagree with you, but the statement "compliance with TERPS all-engines-operating climb gradient requirements does not necessarily assure that one-engine-inoperative obstacle clearance requirements are met" raises my suspicion. The big question I have is, why doesn't it?

Could they be talking about close in obstacles? Remember TERPs starts at 35feet above the airfield.

Talking to several guys I know up at AMC, SDPs aren't very well liked --- at all. I guess they're too expensive. Additionally, if they allow us to takeoff at heavier grossweights, then we don't need as many new C-17s and KC-135 replacements. And this is completely within their playbook. Remember they took the KC-10 out of the cargo equation when they were justifying buying more C-17s.

Who knows, I'm just looking for someone to clarify that italized statement above.

LivingInMEM

Because it doesn't. In a lot of airplanes it may, but in a 727 or a Piper/Cessna twin it does not (some aircraft can barely maintain altitude OEI). Any obstacles that do not penetrate the 200'/nm are not highlighted in a DP, so if you have that you are good to go. In the KC-10, we used to do 2-engine climbout TOLD for all of our takeoffs because we could - if our 2-engine data showed a minimum climb gradient, we were good to go on 3. Many aircraft don't have that kind of OEI performance and many operators don't do OEI climb data - we can't even calculate that if we want to for my current carrier. We calculate all-engine data and we see if we are good to go - but we have no idea about our performance in the event of OEI. That is why they have takeoff mins and Engine-Out DP routings - you follow the normal DP if you have normal performance - but if you lose an engine you go to the OEI procedure which for us is an alternate routing that is based on obstacle avoidance (it is flown ONLY if their is an engine(s) failure) or you fly see-and-avoid.

Tanker-driver

I think some of the issues AMC has with SDPs may have more to do with the vendor than the concept. Last year at AIS, the instructors said something to the effect that the contractor had lapsed in its duties and was not updating the terrain/obstacle database as was required. Never heard Jeppesen's side of the story, but many in the AF have been weary of Jepp products for a while. (seem to work fine for civil operators tho ??) Interestingly, in the -135 community, we have been approved to use SDPs, but currently lack all engines operating performance data, making any advantage gained bu using an SDP effectively moot. I'm afraid that much of our community has blown off a potentially effective tool as a result.