Forum: aviation.stackexchange.com
Tags: <commercial-aviation><takeoff><visibility>
Title: Why can a plane land in zero visibility conditions but not take off in zero visibility?
Question: After waiting hours for a flight departure delayed because of heavy fog, I wonder why planes can perform an instrument landing with no visibility, but cannot take off without a minimum visibility.

Answers:
sents: text: Using a HUD, an airliner can take off with visibility as low as 300’, and land with visibility as low as 600’.
text: Without a HUD, you need 500’ (and appropriate runway lights/markings, plus regulatory approval) for takeoff, and whatever your autopilot Cat III autoland system (along with the landing runway) is approved to for landing.
text: (Or 1800’ for cases of no Cat II / Cat III capability.)
text: As noted, a pure “zero visibility” landing (a Cat IIIc) doesn’t yet exist, because while the autopilot can bring the aircraft to a stop on the runway, some visibility (300’) is still required to taxi clear and get to the parking spot.
text: Thankfully, visibilities below 500-600’ are pretty rare in most places.
text: Not all airports have the taxiway lighting required for low-visibility (typically, below 1200’ lateral visibility) taxi operations.
text: That is an airport limitation, not an aircraft limit.
text: Talking about so many feet of lateral visibility, the actual nomenclature is Runway Visual Range, or RVR.
text: That is reported in feet in the U.S., and often in meters elsewhere.
answer_details: author: aviation.stackexchange.com/users/7532/Ralph J
score: 9
sents: text: Though your question does not explicitly say so, it implies that you're talking about flights that are carrying passengers or cargo for hire, and other answers address that.
text: However, taking your question as explicitly stated, in other words not just air carrier operations, and applying it to U.S. operations, the phrase: cannot take off without a minimum visibility is not always correct.
text: There is no takeoff minimum required for Part 91 operations (private aircraft if you will).
text: In the 2017 edition of https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/media/FAA-H-8083-16B.pdf , you will find on page 1-8 the following: Aircraft operating under 14 CFR Part 91 are not required to comply with established takeoff minimums.
text: Legally, a zero/ zero departure may be made, but it is never advisable.
text: Takeoffs by corporate and personal aircraft without established takeoff minimums were common, though not frequent, in the rainy and foggy U.S. Pacific Northwest weather prior to my retirement, and I have no doubt Part 91 operators still take advantage of that regulatory flexibility.
text: I made many such takeoffs without incident as did fellow corporate and personal pilots at my home field.
text: By the way, while everyone I think understands what they're saying when they say zero visibility, you can always see something, especially if you're sitting down low in a small aircraft.
answer_details: author: aviation.stackexchange.com/users/394/Terry
score: 8
sents: text: They can take off at very limited visibility, and they do.
text: Key is then of course to make sure that no other aircraft are on the runway, and this is in fact how the deadliest crash in aviation history happened: the collision between two B747s at Tenerife Airport in 1977.
text: The accident was not caused by the reduced visibility alone, but as usual by a long chain of individual factors.
text: If all proper infrastructure and procedures are in place, take-off can take place in very low visibility.
answer_details: author: aviation.stackexchange.com/users/21091/Koyovis
score: 3
sents: text: When an aircraft lands in near zero visibility, it is a fully automated process that is actually done without input from the pilot.
text: The pilots are only needed to taxi off the runway and park the aircraft.
text: It is called "Autoland" and many of today's aircraft have it.
text: As of today no manufacturer has designed an aircraft with "Auto Takeoff" but I suppose it is not impossible.
answer_details: author: aviation.stackexchange.com/users/12589/Mike Sowsun
score: 2
sents: text: I have departed in zero-zero conditions (twice.)
text: In both cases, there was another airport very nearby without this problem
text: and I was operating under Part 91.
text: The biggest danger in a zero-zero takeoff, after unseen planes/objects on the runway, is what are you going to do if the aircraft decides to malfunction on liftoff?
text: Lose and engine (or the only engine.)
text: Commercial operations have limits for this, and other, reasons.
answer_details: author: aviation.stackexchange.com/users/26618/Mike Brass
score: 2
sents: text: Under Part 91 operations an aircraft can takeoff with zero visibility (however dangerous that might be).
answer_details: author: aviation.stackexchange.com/users/1520/Steve Kuo
score: 1
sents: text: It all depends upon the equipment the aircraft has board, the infrastructure at the airport that is landing on, and the regulations under which the flight is being conducted under.
text: Aircraft can, under certain circumstances, land in zero visibility conditions.
text: But this requires both the aircraft be equipped to fly a Cat IIIc ILS, approach.
text: The aircrew must have undergone specific training and certification to fly Cat IIIc instrument approaches, and the airport must be equipped with the infrastructure on the ground to support a Cat IIIc ILS approach.
text: As for conducting a zero zero take off, for revenue carrying commercial and charter flights conducted under parts 121 and 135, this is not allowed; minimum visibilities are 1 sm with 2 or less engines and 1/2 sm with more than 2 engines.
text: You may, however, conduct zero zero departures while operating under Part 91 regulations.
text: Zero
text: zero instrument landings are flown by specifically designed auto pilot for this purpose.
answer_details: author: aviation.stackexchange.com/users/15637/Carlo Felicione
score: 0

Summary of the answers:
Aircraft can and do take off in very poor visibility but it is not advisable. Landing in zero visibility is a fully automated process and this process has not been developed for take-off. There are no regulations stating take-off in zero visibility is not permitted.
Planes do take off at zer/zero visibility, especially under Part 91 operations. That said, one difficulty is often the infrastructure of the airport, which may be lacking in terms of facilitation of low-visibility take-off. Also, while there is an automated process for zero visibility landing, there is no such process for zero visibility take-off. Finally, the biggest risk in this kind of take-off, apart from unseen obstacles, is the fear of a malfunction during take-off.