Landing is possible down to 150 ft visibility and no useful vertical visibility using CAT IIIb ILS. This relies on ILS not only for navigating to the runway, but also for maintaining runway centreline during roll out down to taxi speed.

So is it also possible to take off in such weather and if so, how is it done?

(edit) Answer to Who authorizes low visibility takeoff operations for airlines, and what is required? mentions take off is possible down to 300 ft RVR with a "takeoff guidance system". So more specifically, how does that work?

  • $\begingroup$ IIRC if you can't land then you also can't takeoff (to ensure you can get back to ground in case of emergency) $\endgroup$ May 11, 2014 at 16:35
  • 2
    $\begingroup$ @ratchetfreak: That does not seem to be true, see When do I need a takeoff alternate?. And I am asking about when I can land anyway. $\endgroup$
    – Jan Hudec
    May 11, 2014 at 16:42
  • $\begingroup$ @JanHudec on the practical side, the takeoff is just like any other, you just see less centerline stripes / lights than normal. $\endgroup$
    – casey
    May 11, 2014 at 21:26
  • $\begingroup$ @casey: I wanted to know whether there is any automation for the lowest visibility conditions. The other answer you found mentions a "takeoff guidance system", without details. So explanation what that is would be interesting. $\endgroup$
    – Jan Hudec
    May 11, 2014 at 21:31
  • $\begingroup$ @casey that is a related question, not a duplicate. The other question is about the legality of liw vis take off (in the USA, for flights operated under part 121). This questions is about the technical and operationale aspects and seems not to be limited to the USA. $\endgroup$
    – DeltaLima
    May 11, 2014 at 22:08

2 Answers 2


Under the US FARs (at least part 91) nothing special is required to take off in CAT IIIb weather besides an operational (and IFR-legal) aircraft and pilot. As mentioned elsewhere you can legally make that Zero/Zero takeoff where you can't even see the runway under your nose.

It should go without saying that doing so would be incredibly stupid (we (and the FAA) have said so anyway), but from a technical standpoint there's nothing preventing the operation except the knowledge that you might run off the side of the runway into a ditch and bang up your aircraft and passengers.

In terms of what would be required to make the takeoff safely, without running off the side of the runway into a ditch, I'd posit that you would need the same capabilities as you'd need to make the CAT IIIb landing safely: Aircraft systems that let you reliably track down the centerline for takeoff (using the ILS or something of equivalent accuracy for guidance, and runway centerline lights).

You would also need a reliable way to get from the gate to the runway, so taxiway centerline lights & stop bar lights are a must, and probably ASDE-X or its functional equivalent with a controller monitoring it to help ensure you don't taxi into another aircraft.

All of the above is predicated on, among other things, being able to see the lights I mentioned. The "takeoff guidance system" mentioned elsewhere adds synthetic vision into the mix which further enhances safety (and in the airline world allows takeoffs down to 300ft RVR). From what I can glean from the Rockwell-Collins marketing material their HGS seems to be able to provide "follow the green dots" taxi guidance (and presumably runway centerline guidance for the takeoff roll as well), providing redundancy for the lights I described above to help the pilot ensure the aircraft is going where they want it to.

  • 1
    $\begingroup$ With all due respect, I have to disagree with your view "that doing so would be incredibly stupid." The FAA, of course, used the somewhat less abrasive language "never advisable." Even so, I have to disagree with that as well. Perhaps it's a generational thing, but I and others never considered ourselves doing something stupid when we made such takeoffs (all without incident) in everything from single engine aircraft to 747s. The scenario was usually the same, repositioning an empty aircraft under Part 91 from a socked in field to a open field relatively close by. $\endgroup$
    – Terry
    Jun 3, 2014 at 20:05
  • $\begingroup$ @Terry Actual, true 0/0 takeoffs would be incredibly stupid. That being said, I have never seen visibility down to the point where you couldn't see at least a light or two (at night) or where you can't even see the pavement below you. This is partially because you couldn't even make it to the runway in those conditions, so the weather is automatically better than 0/0 if you taxied to the runway in the first place. $\endgroup$
    – Lnafziger
    Oct 18, 2015 at 14:24

The Rockwell HGS doesn't need enhanced or synthetic vision for takeoffs as low as 300' RVR on approved runways. With suitable runway lights, even the HGS isn't required for takeoffs as low as 500' RVR.

Clearly you'd need a takeoff alternate in either case.

You have VERY limited cues with visibility that low, but less is required to fly off of the runway than is needed to land on it, so it is approved and even somewhat routine in places like Salt Lake City and Seattle.

So what IS the takeoff guidance system, or in Rockwell vocabulary, a Head-up Guidance System? It is a HUD very much like in a fighter, with all primary flight instrumentation and guidance visible directly in front of the pilot, so the runway lights and the localizer guidance are superimposed, and the latter is visible even if a dense patch of fog obscures the former.

With enhanced vision, an IR picture from a camera mounted near the HUD is superimposed as well, and depending on the capabilities of the IR, you may never be in weather below Cat I again!

Added: Rockwell HGS promo video

Added: Rockwell Synthetic Vision video

Added: Gulfstream Enhanced Vision video


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