Wednesday, August 6, 2014

0/0 takeoffs for Part 91?

Was at EAA AirVenture (Oshkosh) this past week, and at one of the instrument seminars one of the attendees asked a question I thought would be interesting to others as well. It was involved, but the part I'm going to discuss boiled down to the following (paraphrased):

I am based at an airport with some high terrain nearby that drives up the MDA for the approaches to about 900 AGL. However, I know that I can depart the airport with 0/0 ceiling and visibility. Why is that?

The presenter wasn't able to answer the question (I think due mostly to not understanding what it was), but I was able to help.

First, some background.

As discussed in other blog posts of mine, the MDA (or other minimums) are often determined by nearby terrain. If you have high terrain within a few miles of the airport, on final, you will often have high MDAs for the approach.

This makes sense, and of course 14 CFR 91.175 tells us that if you need to make an instrument approach, you cannot go below the DA or MDA unless certain parts of the runway environment are in sight, as every instrument student learns (I hope).

However, for departure, instrument students are taught that you can legally take off in 0/0 conditions (zero visibility and ceiling at zero feet) and what's more, that's true!

91.175(f) states the standard minimums required for takeoff, such as "aircraft having two engines or less - 1 statute mile visibility", and also requires that aircraft comply with an obstacle clearance procedure.  HOWEVER, this subparagraph only applies to "persons operating an aircraft under part 121, 125, 129, or 135". In other words, NOT part 91 operators, which applies to many of us (including the person asking the question).

Also, from the Instrument Procedures Handbook, page 1-8:

Aircraft operating under 14 CFR Part 91 are not required to comply with established takeoff minimums. Legally, a zero/zero departure may be made, but it is never advisable.

So as a part 91 operator, I have to comply with high minimum altitudes on an approach due to high terrain, but yet I can depart the same airport with zero visibility? Why is that?

The simplest answer is that the takeoff minimums for part 91 are not determined by obstacles or even evaluated in any way. 0/0 is the rule only because it's not prohibited by 91.175. You can make up your own departure minimums if you will.

An examiner once told me to consider three things when thinking about doing something in an airplane - Is it legal? It is safe? Is it smart?

Taking off in 0/0 weather may be legal. It might even be debatably safe-ish, depending on aircraft performance and terrain. It is smart? I don't think so. Not many "outs" in the event of any kind of problem.

What should you do as a Part 91 operator? In my opinion, always comply with at least the established takeoff minimums for the runway.

Looking at a specific example, South County Airport in San Martin, California (E16) has the following departure minimums:

And then has an admittedly lengthy definition of the departure procedure to follow. But the standard takeoff minimums (the ones in 91.175 that do not necessarily apply to Part 91) can only be used if you can maintain a climb gradient of 324 feet per nautical mile (not per minute) to a certain altitude, depending on which runway you depart. Or if you can't meet that, it allows a departure in visual conditions (called a Visual Climb Over Airport, VCOA) with at least a ceiling of 1700 and a visibility of 2.5 miles. This is to get you high enough that once you enter the clouds you can keep climbing and have a good safe cushion over the nearby terrain. If you can't meet that, maybe you should wait a while until the weather improves.

But VCOAs are a good topic for another blog. Fly safe!


  1. In your explanation, you state 'this subparagraph only applies to "persons operating an aircraft under part 121, 125, 129, or 135'. However, the word 'only' does not appear in the regulation. Instrument Procedures Handbook notwithstanding, I contend that 91.175(f) DOES apply to Part 91 operations. Other subparagraphs in Part 91 don't say that they apply to Part 91 operations, it's implicit. Why should this subparagraph have to say that it applies, it's published IN Part 91. Legally speaking, and parsing the words, I think that it does apply.....

  2. MikeM, thank you for the comment.

    I see where you're coming from - you're right, 91.175(f) isn't very well worded, and it could be inferred that since it's in Part 91, it applies to Part 91 operations in addition to the other parts listed. However, this isn't the case. In addition to the FAA's own Instrument Procedures Handbook explicity stating that takeoff minimums do not apply to Part 91, I refer you to the following Regional Counsel letter from 1999:

    Your concern on wording was identified as early as 1967, and the current wording is apparently the "clarified" version!

    Thank you for reading my blog, and please let me know if you have any ideas for topics for future articles. Good flying!


  3. Thanks for the blog.
    At my old airport (KPAO) a fatal accident occurred with a C310 as the pilot attempted a departure in 0/0.

    As I complete my IFR rating now, I always wondered about the legality of 0/0. My CFI thought at least Approach RVR was required but the KPAO tower allowed the 0/0 departure at "pilots risk". My own personal minimum would always be enough visibility to land again if there was a flight issue. Hence minimum approach plate RVR makes sense.

    1. Peter, thanks for reading! The accident report you linked is sobering, and unfortunately we'll never truly know the source of the pilot's spatial disorientation. However, it is well known by IFR pilots that one of the most difficult moments in a flight is that first moment you enter IMC - the transition as you switch from visual to instruments. That's why it's a good idea to get on instruments before you actually enter IMC - so you're already "in the groove".

      With a 0/0 takeoff, you don't have that option. You have to be visual as you roll down the runway, and as soon as you lift off, you're instantly IMC. Dangerous stuff those next few seconds.

      Approach RVR as a minimum at least gives you a little time to get "on the gauges".

      Glad you're completing your instrument rating! It's a tough one but a very worthwhile rating to have. Good job!