Takeoff Minimums

“There’s a mountain there. Can you please check the chart? Also, where’s my phone? Oh, in my pocket” - Bunny One departing 24A in IMC

Taking off under IFR, especially in IMC, can be particularly breathtaking. This is especially true if you’re in mountainous or obstacle-rich terrain, and you could be aiming at a mountain without realizing (*cough cough).

Takeoff procedures are defined under 14 CFR 91.175(f), as shown below. Note that they apply ONLY to aircraft operating under part 121 (airlines), 135 (charters) and others (125 and 129). That means that operators under part 91 (e.g., you in a small Piper flying with your buddy) are not required to abide by them. But should you? Absolutely. If takeoff minimums and obstacle departure procedures (ODP) exist, you should probably fly them (or at least be aware of them). 

Since we are not airline or air charters, let’s focus on those aspects of the regulations that are most applicable to us (i.e., financially challenged part 91 pilots who fly a questionable Cherokee held together by duck tape, superglue, and hope).

Standard Takeoff Minimums

14 CFR 91.175(f) defines weather takeoff minimums based on the number of engines your aircraft has, and require a standard climb gradient of 200 FT/NM (per TERPS). The conditions are the following:

• Single Engine and/or Two Engines: 1 SM visibility.

• More than Two Engines and/or helicopters: 1/2 SM visibility.

So, if you’re a single engine Cessna 172, you should consider your minimums to be 1 SM visibility and a minimum climb gradient of 200 FT/NM. Again, is it required? No. In fact, there are no minimums at all for part 91 operations. You could depart in what we call “zero/zero” conditions (zero ceiling, zero visibility). Is it smart? Questionable. Should you do it? Probably not. 

For everyone but part 91 ops, the regulation further prohibits takeoffs without complying by the obstacle departure procedure (ODP) or an alternative route from ATC. That is a wake up call for us general aviation pilots (GA). The ODP is there for a reason… so let’s read it and use it for our departure planning.

Non-Standard Takeoff Minimums

14 CFR 91.175(f) defines what we refer to as “Standard” takeoff minimums. However, most airports do not align with “standard” conditions. Not every airfield has flat terrain, and so the FAA must publish amended requirements. These amendments are based off of two possible criteria:

(1) obstacles that require a higher climb gradient than the standard 200 FT/NM or (2) reduced visibility conditions.

This latter one (visibility) is dependent on operators’ Operational Specifications (OpSpecs) which are a legally binding operation manual with the FAA (you will not find part 91 operators with one of these, although it would be very impressive and worthy of applause).

Remember the upside down triangle with a ‘T’ in an IAP’s header?

Yeah, that refers to “Non Standard Takeoff Minimums, Obstacle Departure Procedures, Diverse Vector Area, and Low, Close-in Obstacles”. That’s a lot of stuff. But what interests us most is the Non-standard takeoff minimums. For more info

on ODPs, check out this article. 

Example - KASE

Let’s look at an example. Aspen, Colorado (USA) is probably one of the most famous challenging airports in the United States. Let’s assume you are taking off runway 33 and departing using the ASPEN 7 Standard Instrument Departure (SID). The takeoff route is fairly straightforward, but if one notices the Takeoff Minimums, they specify the following

To fly that SID, the weather must be at least 400 FT ceilings and 1 SM visibility, and your aircraft should have a climb performance of at least 650 FT/NM to 13,000 ft MSL. Else, you are not protected by the SID and could collide with terrain and/or obstacles.

Now, are you required to abide by those published takeoff minimums if you're assigned that SID and are flying under part 91? The shorter, legal answer, is no. This is described in the FAA letter Landis 1999. But, to quote a dear friend who is very wise...

"The legality will be determined only after you hit a mountain"

New Takeoff Minimums Page (Not Yet Implemented)

The FAA is modernizing their Takeoff Minimums Page to facilitate user interpretation. The new format, as shown in the sample provided below, has the following sections:

TAKEOFF MINIMUMS. These include the previously available non-standard takeoff minimums as well as a standard takeoff minimums provided a maximum runway takeoff distance. It’s actually kinda cool. Takeoff minimums, per TERPS, are calculated as s function of the departure end of the runway (DER). If you takeoff a lot sooner than that, the obstacles/terrain may be further away than you think. So, the FAA will now provide a maximum takeoff distance based off the DER, if you wish to use standard takeoff minimums. However, these will be provided only if the math works. Some runways may not have this opportunity. In our example, RWY 31 does not have this option, but runway 13 does: Alternative, with std takeoff minimums and normal 200’/NM climb gradient, takeoff must occur no later than 1600’ prior to DER.

DEPARTURE PROCEDURE. The section where ODPs are provided is unchanged. Please follow them, if you can. Else, consider your risk management. 

TAKEOFF OBSTACLE NOTES. This section collects obstacles in two relevant categories for each runway:

1. Low, Close-in Obstacles. These are obstacles lower than 200 FT after the DER (so possibly lower-threat). They used to be listed individually (e.g., “tree, 150 ft, over there”) which made them rather impractical to study. Now, they will be grouped together and defined in 1/4 NM increments from the DER and in relation to the runway centerline (e.g., “right, 3/4 NM away”). The publication also provides the DER crossing height to guarantee clearance with those close-in obstacles with a 200 FT/NM gradient. In the case of runway 31: Crossing DER 43’ above DER elev clears low, close-in obstacles.

2. Takeoff Minimum Obstacles. These are the obstacles that require the amended climb gradient on your departure procedure. These are particularly helpful for part 91 operators like you and me. If you don’t wish to abide by the higher climb gradient, you can review these obstacles and visually avoid them as you depart under IFR. For example, for runway 31: trees, vehicle on road, building 3/4 NM from DER extending 1.3 NM from DER, right of centerline, up to 1078’ MSL, 558’ above DER.

It will obviously take some time to implement these changes (i.e., years), but it’s good awareness to know what’s coming so that we’re not too surprised. Exciting!

Too nerdy? Eh, whatever, you know me.