# Are zero visibility landings practical and desirable for commercial aviation?

With ILS cat IIIc autoland, equipped aircrafts may land on runways without visibility. However they will not be able to safely leave the runway and taxi to the gate. Airports usually close in fog conditions and flights are re-routed to nearby locations. This has a cost for airlines and airports, and an impact on passengers' satisfaction.

(source: Mail Online)

On the other hand technology for taxiing in zero visibility apparently exists: auto-guided vehicles can tow aircraft from the runway exit to the gate. The infrastructure required is not so costly compared to driverless cars now experimented on public roads.

(source: wantdrivinglessons.com)

In the long term airports with autonomous tugs may be interesting as they allow savings by providing power supply while taxing, preventing using aircraft APU and engines when not really required, which in turn can decrease fuel needs and mechanical wear.

Is there a possibility such scenario could happen, because desirable for airlines and airports?

Related (but not duplicates):

• Confirms landing without visibility is "standard business" but that's not zero visibility. according to what I know, no aircraft is certified CAT IIIc – Federico Feb 12 '15 at 7:59
• This has a cost for airlines, and an impact on passengers satisfaction Note that equipping all aircraft with CAT IIIc and auto-guide tractors has also a substantial impact on costs and in turn on passenger satisfaction... – DeltaLima Feb 12 '15 at 8:12
• @DeltaLima: This is true for many of us. I assume some customer groups would appreciate landing at the destination airport in time, regardless of the weather, the price for that wouldn't be relevant for their employers. Exactly like paying toll roads which are a profitable business (in France at least). – mins Feb 12 '15 at 8:43
• @mins But European Law doesn't allow airlines to make that distinction. If they are not flying because the weather prohibited it, then do not have to pay compensation to the passengers for being late. But if there were a means of taxiing in dense fog available, the weather argument no longer can be applied in that case so they become liable to compensation. Even if the costs of using that auto-guided tractor is too much for a low fare airline. – DeltaLima Feb 12 '15 at 8:54
• @raptortech97: Those cars operate in uncooperative conditions. They have to read road signs, for example, and see other car's brakelights and indicators. With cooperation, they would need far less and simpler sensors. (In fact, I wouldn't be surprised if the complexity of one of those car's sensor arrays would exceed that of a modern airliner's. They typically use at least cameras in the visible spectrum, infrared cameras and LIDAR, they may also use ultrasonic sonar, radar, microwaves and passive acoustics in the audible range, plus D-GPS.) – Jörg W Mittag Feb 12 '15 at 14:05

## 1 Answer

Practically there are no zero visibility landings. There is reduced visibility of varying levels. Reduced visibility landings are only allowed when the appropriate ILS equipment is operational. The practical issues are actually not the landing itself but separation from aircraft landing afterwards. On the ground the runway lights are bright enough and close enough for slow navigation. However the aircraft takes longer to clear the runway and this means increased separation between landing aircraft is required. It is this that cases delays as aircraft waiting to land are pushed further and further back.

A ground tug to facilitate speedy removal of the aircraft from the runway makes sense in theory but would be hazardous and the acquisition time wold be non trivial. While an estimated stopping location could be calculated for an aircraft finishing its roll out after landing it would be subject to a very large variation and the tug would have a large distance to cover to get to the aircraft. It would then have to connect and start the tow. The question is whether this wold be quicker than the current arrangement and what the mass penalty would be in terms of changes to the aircraft structure to enable it to use the tug.

Edit: In response to comments I would like to clarify that my point about the acquisition time of the aircraft by the tug is concerned with the non trivial and varying distance the tug would need to cover to reach the aircraft. Any tug configured to pull an aircraft weighing in excess of 100tons would need to be large, heavy, and have high torque to help it safely move the aircraft. These are all things which will reduce its top speed and so increase the time it takes to get to the aircraft from some optimal starting location.

-Multiple tugs Multiple tugs would increase the probability that the aircraft would stop within optimal distance of one of them but would also increase the collision risk and add complexity to the local airflow over the runway.

-Starting locations To facilitate quick response and removal of the aircraft from the runway the tugs would need to be located close to hand. However they cannot be on the runway and would be required to be back from the edge by a significant distance. When you consider the finite number of taxiways and the sheer variation in aircraft roll outs this presents a very wide range in possible locations the tug would need to get to with a consequential increase in response times.

-Aircraft Rollouts When an aircraft lands it typically uses a small amount of remaining velocity to keep it rolling and move off the runway. This would almost always be quicker than waiting for a tug.

-Hybrid tug system A hybrid system in which the aircraft uses residual speed to clear the runway and meet a tug has some advantages in terms of optimal tug positioning however it reduces the advantages in fuel consumption and increases the amount of vehicles independently moving around the airfield.

• Radar and GPS should have no difficulty directing the tug to the landed plane so I don't think that's really an issue. – David Richerby Mar 22 '15 at 18:43