Let me restate it one more time. A transport category aircraft suffering an engine failure on takeoff will likely NOT meet TERP's climbs requirements and isn’t required to do so. The AIM alludes to this in 5-2-6(e)(4) by stating that the pilot should "consider the effects of degraded performance and the actions to take in the event of an engine loss during the departure." The Canadian supplement and ICAO PAN-OPS state it more clearly that IFR SID's and departure procedures are based on normal, read all-engine performance, and not one-engine out performance.
As you mentioned, TERP's climb requirements for DP's are based on a 40:1 obstacle identification surface (OIS) beginning no higher than 35 above the departure end of runway and continuing to the minimum altitude for enroute operations. If no obstructions penetrate the 40:1 OIS then the standard IFR climb gradient of 200 ft/NM applies. This provides at least 48 feet per nautical mile of obstacle clearance. If obstacles penetrate the OIS, then the DP climb gradient will be raised a sufficient amount to regain the 48 ft/NM clearance. Careful note must be given here. There could be obstacle which would require higher than standard climbs but only to heights less than 200 feet above the runway. In this case, higher than standard climb gradients are NOT provided
Like you said, Part 25 aircraft do not provide all engine climb performance data in the AFM. When the performance rules were first written for the first jet transport aircraft, one engine-out performance was considered more restrictive than all engine performance data. This engine out performance data was used to develop the takeoff flight path concept discussed above. The climb gradient data from the AFM is used ONLY to construct the net takeoff flight path as described above and cannot be used in meeting TERP's criteria. Any attempt to use the climb gradient charts from a Part 25 AFM in determining TERP's obstacle clearance would be using this data in a manner for which it was never intended and never approved for.
There are several reasons you cannot use AFM 2nd segment climb data in meeting TERP's criteria. First, all the one engine-out climb flight path data (1st, 2nd, and final segment climb charts) are only good to 1,500 above the runway and CANNOT be used to the heights demanded of certain DP's such as is the case of KASE, 7,800 ft to 14,000 ft. 2nd segment climb data is generally only valid to 400 ft above runway, the point where 2nd segment ends. Second, the differences in climb terminology. Most 2nd segment climb gradient charts in AFM's give the available NET climb gradient so that when you apply this to the flight path charts or computer program you get a resulting NET flight path. TERP's climb requirements are based on actual performance, NOT an already an already reduced NET climb gradient. There's the consideration of 5 minute limitation on takeoff thrust. Many DP's require climb gradients to significantly high altitudes that would exceed the limitation on takeoff thrust, not to mention a shallowing climb gradient due to density altitude changes as you climb. Remember if you try to use 2nd segment climb, you'll only meet that climb gradient if you keep V2, takeoff flaps, and takeoff thrust and that climb gradient is generally valid only at 400 ft above the runway. Finally, as we said above, TERP's performance is stricly considering normal aircraft performance, not an emergency situation such as engine out climb.
FAR 25.121 does not specify a minimum certification (gross) climb gradient for the enroute configuration beyond 1,500 feet AGL (end of the takeoff path under FAR 25.111). However, FAR 25.123 does require the determination of the one-engine inoperative and two-engine inoperative (for 3-engine or 4-engine aircraft) enroute flight paths. These enroute flight paths must be determined at each weight, temperature, and pressure altitude within the aircraft's operating limits and will have a gradient reduction applied.
Typically, the AFM will state that the net enroute climb gradient chart(s) are presented for pilot reference, FAR 25 requires their inclusion in the AFM for use in determining obstacle clearance for the net enroute flight path as required under FAR 121.191 (one-engine inoperative) & 121.193 (two engine inoperative) or FAR 135.381 (one-engine inoperative) & 135.383 (two engine inoperative).
So the two big questions are as follows:
1. How does one compute climb requirements above 1500 AGL when no data is available from the manufacturer?
The net enroute climb gradient chart(s) will provide you with the available net enroute climb gradient for your current weight, temperature, and pressure altitude. With this information, you can 1) review the entire route and ensure you have a positive net enroute climb gradient clearing all obstacles by 1,000 ft, 5 SM either side of the intended route, or 2) pick the most critical point on the route, assume the engine fails at that point, and continue with a net enroute flight path that clears obstacles by 2,000 ft, 5 SM either side of track. You may assume normal fuel consumption using either method. Using method 2, you must also designate as an alternate airport the airport you use after the engine fails. That airport must meet the required alternate weather minimums. You may break up the route into a series of segments with the most advantageous drift down route and alternate for each segment.
So where do you find the obstacle data for the planned route? United Airlines has a world wide computer obstacle database and dispatch program this purpose. For us, sectional charts, Grid MORA's MEA's, MOCA's, would be good starting points. This is a dispatch function only. If the engine fails, you're still expected to land at the nearest suitable airport.
2. How in the world can any aircraft legally depart Aspen under any circumstances? How do the BAC 146's, Dash 8's, and other commuter aircraft types legally depart from ASE? The BAC 146 might meet the DP if it lost an engine if was going to DEN, but how about to ORD? The Dash 8's and other prop commuters? It's inconceivable to me that they'd meet the DP with an engine out. I just can't see them outperforming a Lear 31A on one engine. These are all FAR 121 air carriers with extensive FAA oversight. Yet they takeoff every day from ASE and in bad weather. The same could be said for other airports like Reno.
The DP is a normal performance procedure only. Even the AIM alludes to this by specifying that the pilot consider the effects of reduced performance following an engine failure on a DP and have alternative actions available.
In answer to this specific question, using a sample airport analysis for ASE runway 33 and for a Lear 35 the climb limit weight at 80 degrees F is 16,030 lbs. This weight limit meets 1st, 2nd, and final segment certification (gross) climb requirements. The runway 33 limit weight is 14,770 lbs. The runway limit weight meets the requirements for takeoff distance (all engine & one engine inoperative), accelerate stop distance, brake energy limit, and net takeoff flight path obstacle clearance utilizing a special engine out departure procedure. This procedure does follow the valley out to a holding pattern on the DBL R-244 at 15.0 DME, essentially in the valley over Carbondale, CO. At this weight, 14.770 lbs., you will not meet the DP climb gradient to 14,000 feet with one engine inoperative. The 2nd segment net gradient about 4%. Still, an FAR 121 or 135 operator of this Lear 35 would be perfectly legal departing Aspen at this weight and temperature, assuming that no other Subpart I dispatch requirements are more restrictive.
'Sled