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Obst. Dep. or "SID"

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Well-known member
Dec 30, 2001
I know that this question has been posted many times, I can't find it right know.

Lets use KASE for an example. On the LINDZ 4 you have to make the gradient if the WX is below 3100-3. Here is the question. If the WX if 3000 Bro and 10 Miles this is VFR WX. But you can't meet the climb grad. Can you accept the LINDZ 4?

This is my thinking; VMC/IMC make no difference you are on an IFR flight plan. Therefore would have to meet a climb Grad with WX of 3000 and 10. If you can't make the Grad. you have to fly the Obsticle Departure (by the way the LINDZ and the Obst. Dep. are the same) b/c it is VMC WX below mins for the "SID"

So you are sitting on R/W 33 and get cleared for the LINDZ 4 with WX of 3000-10. Should you say "No can do" and ask for the O.D.?

Please give spific references to CFR's and TERRPS

The Lindz Four IS an obstacle departure. You're asking about the departure proceedure (DP) published on the back of the 13-1 plate in the takeoff data section below the airport diagram. This departure is the same as the Lindz; read the text and compare it.

If you can't meet the climb gradient, should you really be departing? This is something to think about before you fly to that airport, not before you leave.

Former SID's and obstacle departures are all combined now as Departure Proceedures. You'll note that a comparison between the climb gradient depicted in the takeoff data for ASE, and the Lindz Four, shows that the required gradient is the SAME.

Under IFR, the PIC is responsible for terrain and obstruction clearance until this responsibility is assumed by ATC in the form of radar vectors. A VMC departure may allow for terrain clearance by maneuvering, but may not take into account the ability to maneuver in a like manner with the failure of a powerplant. Under Part 91 this isn't an issue unless something goes wrong. At such point compliance with 91.13 and 91.103 will be considered. Under 121 or 135, the climb gradient must be met and the proceedure flown.

TERPS criteria, upon which the DP is predicated, provide for terrain and obstacle clearance. Should you elect to provide your own, you may at some point be required to show how you determined this. In the case of a clear visual departure, this is a matter of showing that you saw the rocks and went around them. This can be done under Part 91. For operations under Part 135 or 121, the operator must show an alternate means of compliance. Failing an exhaustive study of clearance criteria, as provided for in TERPS, an operator may have a hard time making a case for an IMC departure without full adherence to the DP. Further, as it's already published, there is no reason not to use that proceedure.

If the climb gradient cannot be met with all engines turning, seriously consider altering your flight operation. This may mean making an extra trip, removing fuel, leaving baggage, or whatever must be done in order to make a safe and legal departure. If the gradient cannot be met on two or more engines, it can't be met on less. This presents a dillema during a power loss. In the case of ASE, referring to the named DP won't excuse you from climb gradient requirmements any more than referring to the text description on the takeoff minimums data section will relieve you from those of the named DP (Lindz). Six of one, half dozen the other, and the hills haven't moved. You still must clear them.

See the excerpt from FAA Order 8400.10 copied below.

FAA Order 8400.10, Vol 4, Ch 3, Sec 1, para 927E:

E. Takeoff Minimums. TERPS criteria is based on the assumption that the airplane can climb at 200 feet per nautical mile (approximately 30:1) to the minimum enroute altitude through the takeoff flightpath.

(1) When obstacles penetrate the obstacle clearance plane, the airplane must be able to climb at a steeper gradient or to use higher than standard takeoff minimums to allow the obstructions to be seen and avoided under visual conditions. Authorizations for lower than standard takeoff minimums are based on the operator adjusting airplane takeoff weight to avoid obstacles in the takeoff flightpath if an engine fails on takeoff. POIs shall not authorize operators who do not prepare an airport analysis and perform obstacle climb computations to use lower than standard takeoff minimums. POIs may approve a system in which the operator makes obstacle clearance computations and performs lower than standard visibility takeoffs on specified runways, as opposed to all runways.

(2) The criteria for TERPS does not take into account whether or not the aircraft is operating on all engines. Operators must either show compliance with TERPS criteria with an engine out or have an alternate routing available for use in case of an engine failure. Specific guidance for approval of these procedures is in development and will be included in this handbook at a later date.
Suppose you are now departing from an uncontrolled airport in Class G airspace. The weather if VMC, it is a 135 flight and you have an IFR flight plan that you will pick up once airborne.

Under IMC this type of departure without a clearance wouldnt be legal as maintaining VMC if departing without an IFR clearance is required under 135. So if it IMC you would have to get a clearance and follow any DP for that airport.

But what if departing VFR in the situation above? Do you have to fly the departure procedure? My thinking is you are legally flying VFR and therefore responsible for your own terrain clearance and therefore it is not necessary to fly the DP
The obstacle DPs are only for the pilots safety and most time ATC may not even know about them. You probably know this, but your ops specs more than likely authorize you to depart VFR and pickup IFR in a certain amount of distance. There are exeptions though.

As far as VFR departure, you can avoid lengthy obstacle DPs by just going straight to your route, but only if ATC doesn't assign one. Thats unless your flying a graphic DP. There is really no way to avoid those since it makes ATC's job much harder.
Fun subject, this one. Many professional pilot's do not understand it well. Here goes my take:

The TERPS folks perform an obstacle identification surface (OIS) on every airport witha published IAP. This OIS is a 40:1 slope 360 degrees from each runway, from 400' to the MEA. (Minimum IFR altitude in ATC parlance) The FAA assumes no turns will be made untill 400' HAA. Do not ever begin a turn in IMC prior to reaching 400' for precicesly this reason, unless the DP say "turn as soon as practicable" any DP you fly with this "early turn" rule should have mandatory departure minimums of 400-1.

If the airport has no OIS obstructions, there will not be a published DP. You may proceed on course once reaching 400' HAA. Any obstacle that protudes into the OIS slope will result in the TERPS specialists publishing a DP. Either a minimum climb gradient or a textual description. ("Fly runway heading untill reaching 2000'.) This OIS only goes to the MEA, there could very well be secondary obstructions such as a mountain range. If you are uncertain, remain established on a low-altitude airway until clear of any obstructions. This OIS is the 200 feet per NM you hear tossed about. It is made up of 152' per NM, plus an arbitrary 48' additive. (3.3% gradient) Part 25 only gives you 2.4%, there are some jets that under certain weights and temps fall between the 2.4 and 3.3, the Lear is not one of them.

Now as far as climb gradients go, the Learjet has performance charts published, You should be able to easily compute the climb gradient for given conditions. Going back to your question about the LINDZ 4 out of ASE, I don't have it in front of me, but here are the basics. You have to meet the departure minimums or make the climb gradient. [C57(b) & 135.379(d)] You talked about the possibility of departing VFR, but your OPS SPECS probably say under B33 that this is an option ONLY if the airport has no operating ATC facilities and it is not otherwise possible for the flightcrew to obtain an IFR clearance. My understanding here, and its difficult to find the exact reference, is that you have to meet the climb gradient requirements or higher than standard takeoff minimums or be able to climb VFR from the airport surface to the MEA. Your ASE example does not meet these requirements. This is an area that even extremely experienced pilots are somewhat shaky on. Your company will push you to do all sorts of stupid things in these mountain bowl airports, if you have any doubts, DON'T! Irrespective of the regs, I will not ever shoot a procedure at ASE, EGE, and TEL unless it's DAY/VFR (SFC to MEA) If they don't like it, they can replace me with a lunatic.

Perhaps TIS would like to comment on this one, He's very good with the references, and has access to part 97, which I don't. Bruce?


"If the airport has no OIS obstructions, there will not be a published DP. "

This isn't true. The criteria you describe are used to determine a diverse criteria departure. In the case of diverse criteria (nothing obstructing the 40:1 plane), then no obstacle departure proceedure will be provided. However, proceedures for expediting the flow of traffic or traffic management may also be used, and a departure proceedure published. This is often done even when no obstacles penetrate the diverse plane. Formerly, obstacle departures and standard instrument departure proceedures were separated by classification, however, now they're all DP's.

Lack of a departure proceedure only indicates that a turn may be made in any direction from the departure runway, and a climb made using the standard gradient, without any interruptions into the 40:1 plane.

I have absolutely no problem flying into Eagle or Aspen, or any of the other airports in that region. I've met individuals who do, who are uncomfortable with the prospect, or who won't do it with any weather. I respect their decision, but it doesn't mean flying into or out of these locations is dangerous or unwise. Quite the contrary. It isn't. I've flown approaches to each of the airports mentioned, to minimums on a number of occasions, and have flown departures into instrument conditions from those same fields without complaint. I would do so again.

I am not a lunatic. A good share of my career experience has been spent in close proximity to terrain, primarily mountainous terrain; I'm comfortable with it, but that doesn't make me or any other pilot who uses these flight checked and tested proceedures, a lunatic. If the aircraft can meet the departure criteria, and it's available to fly, there is no reason not to fly it.
Excellent point AVBUG, my home airport has published climb gradients on several of the DP's, all of which are predicated on ATC routes. When I said "If the airport has no OIS obstructions there will be no DP.", what I should of said is that if there is a DP gradient provided, it will be for ATC purposes and not obstacle clearence.

Dude, I did not call you a lunatic. I was refering to those poor misguided morons on the 135 side of the house who will do anything whether it is legal or not. You know the kind of people I'm talking about. The fact remains that most turbine powered aircraft with two engines being operated for hire, cannot legally depart many of these mountain bowl airports unless it is VFR from the surface to the MEA. There are plenty of folks who either through ignorance or willfull negligence, will do whatever is required to get the job done.

Your terrain flying skills are to be commeded. Most of us do not posses your level of experience and comfort in these areas, and as a result are going to approach them conservatively. Anyone who has flown a Lear 55 out of Telluride and seen the runway left at the V1 call realizes that even part 25 numbers are sometimes highly suspect. The "average" pilot does not posses the skills to safely manage the risk of IFR approaches to minimums in a mountain bowl airport. The high rates of descent and maneuvering requirments after breaking out would constitute a situation where normal safety / human factors margins are slim to none.

Let's keep correcting and questioning one another. Bring it on! Threads like this are what make this board a tremendous resource. I love it when I get to learn something new or am reminded of something I forgot.


PS- Hey avbug, what kind of airplane do you currently fly?
I saw something yesterday I thought was interesting.

As I am taxiing around CRW I see a GIV or GV taxi into position and begin his takeoff roll on RWY 33. It was an awesome sight but RWY33 is only 4750ft long while the other runway is 6300ft so I watched to see where he would rotate at. I was at the 1000ft remaining sign and he rotated just past my position. I can only assume that his weight was light and that a GV could still clear the towers on the hills just north of the airport if he lost an engine. All I know is that it would have been a horrific sight to seem him do a rejected takeoff and spill off the end of 33 into the valley below.

I'm I wrong thinking the 6300ft runway would have been a better choice?
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I guess that would depend on the winds, and other factors. All things being equal, the longest runway is generally best. However, factors such as the position of the sun, surface winds, terrain gradient, etc, all combine to sometimes make a shorter runway the better runway. Consider that even though an aborted takeoff may not be viable, continuing the takeoff might. It's impossible to make judgement without a lot more information.

Ljdrvr, I don't actually fly. I paint easter eggs for a living. With the holiday less than a year away and kids getting more violent every year, I'm running way behind. (I used to deliver the eggs, too, but I gave it up for Lent).

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