Anything that is not specifically prohibited by the Federal Aviation Regulations is therefore allowed. There are a number of things you can do with an airplane that are legal, but at the same time may be dangerous — the IFR low visibility takeoff is one of those. Not everything that is legal is also smart.
The writer of aviation regulation 91.175(f) must have been a master of slight-of-hand. The opening line is written in a peculiar, if not deliberately misleading way. The rule states: ‘Unless otherwise authorized by the Administrator, no pilot operating an aircraft under parts 121, 125, 127, 129, or 135 of this chapter may takeoff from a civil airport under IFR unless weather conditions are at or above the weather minimums for IFR takeoff prescribed for that airport…’ FYI: Pilots who operate under parts 121, 125, 127, 129, or 135 are airline and air charter pilots — they would not be looking in part 91 in the first place, since part 91 rules do not apply to their operations.
WAIT, IT GETS BETTER
The list of operators who must follow ‘prescribed takeoff minimums‘ does not include part 91. Translation: Part 91’s rule on takeoff minimums excludes part 91 operators. Was this regulation written to deliberately confuse the part 91 pilot into believing that, for IFR takeoff, they must have, [91.175(f)(1&2)] one statute mile visibility when the airplane has two engines or less and at least one-half statute mile when the airplane has more than two engines? I don’t claim to know the motivation of the regulation writer, but if part 91 operators are not included in the list of operators that must abide by these rules — then part 91 operators have no takeoff minimums.
A part 91 pilot can takeoff legally with a ‘zero’ ceiling and zero visibility.
The most common example of the zero-zero takeoff would be through ground fog. The fog may only be a few hundred feet thick and soon after takeoff you would break out into beautiful sunlight — but you could not turn around and come back — you would have to be going somewhere that you knew the weather was much better.
Uncommon Sense: That being said — please don’t elect to make a zero-zero takeoff … even though it’s legal. Your instrument instructor may have you practice a ‘hood takeoff’ just to prove that it can be done — but a zero-zero or extremely reduced visibility takeoff should be avoided.
A LITTLE KNOWLEDGE…
When a part 91 pilot learns that they really are not subject to any prescribed takeoff minimum they can easily overlook ‘departure procedures.’ The NOS (government) charts and the Jeppessen charts both have Takeoff Minimums and Departure Procedures listed together. If a part 91 pilot sees these instructions and thinks, ‘these don’t apply to me — after all, I’m part 91 and part 91 has no takeoff minimums‘ This assumption is only half true. Part 91 pilots might not have strict minimums but every pilot regardless of which part they operate under must understand and comply with any departure procedures that are printed.
Departure Procedures for airports are listed in the chart books. NOS charts have a separate page in the front of the book that list all departure procedures. NOS uses the letter T inside a triangle to alert pilots to the fact that departure procedures are written for a particular airport. You will find the T-triangle symbol at the bottom of the approach charts. Jeppessen charts have the departure procedures written on the back of the airport diagram page for the airport involved.
Example: The departure procedures from the Birmingham Municipal Airport read in part, ‘Runway 5, climb runway heading to 1700 feet before turning on course.’ Why 1700? The Birmingham airport is in a valley — if you turn too soon, you will hit a ridge! Be advised, the mountain ridge does not care which ‘part’ or what kind of ‘operation’ you are under. A part 91 pilot operating with the notion that they are subject to no takeoff minimums and therefore does not need to worry about departure procedures – could have a rather unpleasant surprise.
CAUTION: Departure procedures are usually not included in the IFR clearance! The departure procedures are considered part of the enroute portion of the flight, so when the controller says that you are ‘clear as filed‘ they are assuming that you have already read the departure procedures — the controllers will not read them to you!
As a part 91 instrument rated pilot — with 150 flight hours or more — you can legally takeoff with no visibility and/or no ceiling at all, while a Boeing 737 airline captain with 10,000 hours sits waiting for the takeoff conditions to improve. While you taxi past that airliner on the way to the runway ask yourself — ‘What’s wrong with this picture?’