Second Segment Climb

[dispatchguy]

Note, however, that the gross gradient required of 2.4% is decreased by 0.8% for the net climb gradient required, and that is where the 1.6% climb gradient required comes from...

Its this NET gradient, that must clear all obstacles in the departure path...

 

[soarby007]

second segment climb

The second segment requirement is one thing. This is a certification requirement and you have to make that, one or two engines. Yeah, the airplane physically has two engines out there and the requirement is 2.4%, but if one of them quits, it still means 2.4%.

The requirement out of Eagle and Aspen is another. If you can't meet the departure weather requirements out of Eagle, i.e. 5400-3, then you have to comply with the departure procedure climb requirements, not til you reach VFR conditions. That's what it says. To wish it said something else is playing with fire.

Most jets operate legally out of these airports, because 90% of the time takeoff minimums are met. It's not real smart to take off out of those two places IFR if you can't meet these requirements. I know that if the tops are 3000'agl then it's probably no big deal, you can see the mountains and avoid them, but the departure requirement doesn't say that. Most mountain airports seldom have tops @3000'agl, unless it's fog. The clouds are usually higher than the surrounding mountains, or close to it. This is not an absolutely true statement of course, there are lots of exceptions, but generally if it's cloudy, IFR, it's either real low and not worth taking off, or the tops are above 3,000 agl.

I've been told that only 4 planes can make that takeoff gradient out of Aspen on one engine, Falcon 50, G-IV,V, and I forget what the other one is, some other Falcon. Don't know if it's true or not.

 

[Lead Sled]

2nd segment revisited...

This whole topic is perhaps one of the most misunderstood aspects encountered when you transition into flying jets. Let me try to explain it the best I can.

Second segment climb is part of a certification requirement under FAR 25 (Sec. 25.121 Climb: One-engine-inoperative). In each "phase" of the takeoff, takeoff-gear down, takeoff-gear up, and takeoff-final, a Part 25 transport category aircraft must exhibit a minimum one-engine inoperative climb gradient (rise/run) except for those phases that involve level acceleration.

These phases or segments must be specified by clearly defined changes of configuration, thrust, & speed. They begin from lift off and continue until the aircraft is at least 1,500 feet above the runway elevation or to point where transition to the enroute configuration is complete (clean, MCT thrust, 1.25 Vs). This is known as the "Takeoff Path" of the aircraft.

The gradient of climb is depended on the number of engines installed, giving greater safety margins to those aircraft with more engines (the idea is more engines means a heavy, less maneuverable aircraft, and thus should have greater minimum climb requirements) For a two-engine transport category aircraft, the 1st segment (lift-off to gear retraction) requires a positive gradient out of ground effect. A 2.4% gradient is required from gear retraction to 400 ft. in the takeoff configuration, gear up, takeoff thrust, at V2. At the end of the final segment, clean, MCT, 1.25 Vs (otherwise known as "enroute configuration"), the aircraft must capable of a 1.2% climb.

Both FAA approved Aircraft Flight Manual and the FAR's are going to require the pilot/operator to limit takeoff weight so as to meet this certification requirement. For Part 91 operators of aircraft certified after 9/30/58, it's 91.605(b)(1) and for Part 135 operators it's 135.379(a). There will also be a limitation in the AFM limiting the takeoff weight such that these one engine-out climb requirements are met. Usually it's in the form of a statement such as "the maximum allowable takeoff weight shall not exceed that shown in the takeoff weight limit chart", but that can vary between manufacturers. So you must always meet your 2nd segment climb requirements along with the minimum climb requirements for other segments. Comply with the AFM restrictions and the approprate charts in this matter and you'll be ok.

So far, most everyone gets it correct up to this point. It's when you start Taking obstacle clearance and TERP's requirements that folks tend to get things screwed up. FAR 25.115 defines the takeoff flight path. For each weight, temperature, and pressure altitude the manufacturer must determine the one engine-out takeoff flight path. They must use the same segments as defined in the certification climb requirement above. The takeoff flight path begins at end of the one engine-out takeoff distance (35 feet above the runway or a point known as "reference zero") and continues to the end of the takeoff path described above (1,500 feet or transition to the enroute configuration complete, whichever is higher). This is the actual performance of the aircraft as demonstrated from flight testing based on procedures developed for "in-service" operation, flown by crew's of "average skill", with allowances for any time delays that may be expected in service (25.101).

The net takeoff flight path represents the takeoff flight path described above diminished by a percentage of climb gradient depended on the number of engines installed, -0.8% or two engine aircraft, -0.9% for three engine aircraft, and -1.0% for four engine aircraft. Since both the actual (gross) takeoff flight path and the net takeoff flight path begin at 35 feet, you can see that net flight path will be 0.8% lower (2 engine aircraft with an engine inoperative) than the actual flight path giving a difference of 48' per nautical mile between the two flight paths. The concept here is that the difference between the actual flight path and net flight path yields an ever increasing spread between the two path. At 10 miles, they'll be 480 feet separation between the two flight paths. As you'll see below, obstacle clearance is based on the net flight path to as to ensure an increasing margin for obstacle clearance as the aircraft climbs further from the runway.

The net takeoff flight path is used in meeting the one-engine out takeoff flight path requirements of FAR 121.189(d) and FAR 135.379(d) for turbine aircraft. This regulation states that the net takeoff flight path must clear obstacles by 35 feet for those obstacles 200 feet either side of the flight path inside the airport boundaries and 300 feet either side after passing the airport boundaries. Each operator must perform a detailed analysis of all obstacles, and using either the AFM flight path charts or computer-based performance programs demonstrate that they can meet the above obstacle clearance requirements. Obstacle data is obtained from a variety of sources including airport obstruction charts, USGS terrain charts, etc. It's not something you are going to do on pre-flight. You'll have to obtain this obstacle data from a engineering source like Jeppesen Ops' Data. They'll give you obstacle data for a particular airport/runway and any special engine-out turning procedures that may need to be applied. If Jeppesen Op's Data has the AFM data, they can do all this ahead of time and print out an "Airport Analysis". From this analysis, you have the maximum weight allowable for that airport/runway in terms of a runway limit weight and a climb limit weight for a given temperature. Correction factors are provided for non-standard conditions, wind, A/I on or off, etc. The airport analysis is the method used by the FAR 121 air carriers.

Now, let talk TERP's, DP (a.k.a. SID) and climb performance. First, the one engine-out obstacle clearance requirements stated above and the TERP's IFR obstacle clearance requirements are two entirely different subjects! They are not related in any way. A transport category aircraft suffering an engine failure on takeoff will likely NOT meet TERP's climbs requirements and IS NOT REQUIRED TO DO SO!!!!!!!!!!! (enough emphasis?) This is where folk get things wrong. 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.

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

The problem with a Part 25 aircraft is that we are not provided with all engine climb performance data in the AFM. When the performance rules were first written for the first jet transport aircraft (SR-422), 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 we discuss 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 (some manufacturers have gone beyond this point up to 3,000 to 5,000 feet) 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.

'Sled

 

[Ty Webb]

Sled:

Thanks for a very informative post, but you lost me when you said [and I'm paraphrasing here] that we should not use the second-segment net climb info [and presumably Final Segment gradient] for TERPS clearance, since that is pretty much all the data we are provided, other than a VSI, altimeter, DME and a four-pound wristwatch.

Also, all those after-lunch classroom sessions at FSI recurrents that involved the use of "the BIG book" (AFM), graph paper, number two pencils, and many cups of coffee would seem to have been wasted, since we were using that same information to plot our escape from simulated obstacles upon departure from barely-suitable and hypothetical airports . . . . .

So, how do YOU plan your departure, given these vagaries?

And, thanks again for taking the time to post. I am printing out your previous response and saving it; should I find myself out of the 121 environment, it will no doubt be a very useful refresher.

 

[soarby007]

Hey Sled, good job.

 

[CaSyndrm]

I posted on 2nd segment climb while thinking of SID climbs. I think subjects have been mixed a little on this thread. Second segment ends at 400' which isn't very far past the end of the runway at Aspen so I still stand by my climb statement excluding the first 400'. Show me a reg in 91/135 that says you have to maintain SID climb gradient performance under single engine conditions, that's what I tried to convey in my original post.

 

[soarby007]

Hey Sled,

I guess to clear up one more thing in my head. Specifically,departing Aspen, at less than 1000-2 or 3100-3, there is no requirement to maintain 460'/nm to 14,000', on one engine, is that correct?

 

[Ty Webb]

Second segment ends at 400' which isn't very far past the end of the runway at Aspen

I guarantee you that if you "blow a motor" at V1 departing ASE, 400' AGL is not going to be anywhere near the end of the runway . . . . especially in the summer.

If you have your 2.4% that is 152 ft per n.m., so if you are very good, you might be able to get there inside of 3 very . . . . long . . . . . seat-cushion . . . . sucking . . . . . miles.

 

[Lead Sled]

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 does United Express and others flying 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? I doubt it. 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.

Does a 121 or 135 operator have to meet the takeoff minimums? Yes, under 91.175 and this does include the DP climb gradient unless weather conditions allow using the see & avoid method. But the required climb performance is based on normal performance, all engine performance. The same goes for Part 91 operators too, if they accept the DP, but again only with all-engine, normal performance.

The Jeppesen Airport Analysis reports provide escape maneuvers that are not published in any charts we normally carry on the aircraft. In fact, the escape maneuver from Jeppesen at ASE essentially follows the valley out to GJT. Hence the reason for VMC.

Sled

 

[fly4free]

you are confusing 2nd segment with TERPS

First of all climb gradients in the US are for 2 engines not one.

This is actually correct...most of you in this discussion are confusing second segment climb requirements with SID or DP climb requirements.

SECOND SEGMENT HAS ABSOLUTELY NOTHING TO DO WITH TERPS DP CLIMB REQUIREMENTS.

There are near obstacle and distant obstacle clearance requirements but these are not related to 2nd segment or DP climb gradients. As someone mentioned there is different clearance requirements if the obstacle is within the airport boundary or not...in order to calculate this, though, one must have the distance from the departure end of the runway of the obstacle (in feet) and the height above the runway (in feet). But this is still a different issue.

Ponder this: IFR airports that have no DP have been surveyed on a plane of 152 feet per nautical mile for obstacles...if no obstacle penetrates this plane then no DP is required to be published...the minimum climb gradient is 200 FPNM (3.3%) in this case allowing for a 48 FPNM buffer...any multi engine jet that just meets the part 25 minimum 2.4% second segment requirement would not be able to meet even the minimum TERPS climb gradient...so this meens that you can't takeoff until it's VFR? no that's not what it meens...it meens that one must have a plan B in case one engine quits.

How about this...a high performance single-engine turbo prop wants to depart KVNY on runway 16R on the Newhall six DP (6.2% climb gradient)...the aircraft can confortably maintain the gradient under most normal conditions...but what if the only engine quits...this aircraft will not maintain the gradient in it's emergency condition...likewise, the multi-engine jet that looses one will not be able to maintain the gradient in its emergency codition...even at nearly sea level.

I will end with this...the Gulfstream GV manuals and charts are the newest most complete sources of performance data any pilot could ever need. And they make a disclaimer in the charts that DP gradients are not "required" to be met on SE ops, part 91 or 135.

You guys preaching that DP gradients must be met have no regulations to back up your claim...part 25 doesn't work...large and turbine powered aircraft takeoff performance requirements doesn't work either because that is all engine requirements.

Lets hear it????