De-icing fluid is metered out of the rig by the litre against an aircraft type and a contamination level, because it costs four pounds a litre and the figure is audited. Stand 9 costs us four hundred more every time.
I have driven a de-icing rig at a regional airport for fourteen winters.
The metering is the whole of this, so here it is.
The rig carries type one fluid, which is hot and thin and takes the contamination off, and type two or four, which is thicker and stays on the wing to stop it forming again for a known number of minutes.
The flow meter on the boom counts what goes out. It records against the aircraft registration, the stand, the fluid type, the mix and the ambient temperature, because the mix strength depends on the temperature and the holdover time depends on the mix.
That record is not for the accountants, although they use it. It is a safety record. If an aircraft has an incident on departure, the first thing anybody wants is the de-icing log.
There is a figure for every aircraft type. A regional jet in light frost takes somewhere around three hundred litres of type one. Heavy contamination and a bigger airframe, more.
On stand 9 we use about four hundred litres more than on any other stand.
Same aircraft type, same contamination, same temperature, same crew. I have compared like for like across four winters of logs, because the figures are on a shared drive and anybody can look.
It is not one operator. All six of us come out heavy on stand 9.
Where it goes on.
The extra is all on the port wing.
You work an aircraft in a pattern: leading edge outboard to inboard, upper surface, then the same on the other side, then the tail. You know how long each pass takes and how much it uses because you have done it a thousand times.
The port wing on stand 9 takes about two extra passes to come clean.
What clean means, because this is where it stops being about fluid.
You are looking for a clean, wet, shiny surface. Contamination shows as texture: frost is dull and white, and clear ice is the dangerous one because you have to look for the distortion of the light rather than a colour.
On the port wing on stand 9 there is a patch, roughly two metres by one, about a third of the way out from the root, that stays dull after a pass that has cleaned everything around it.
Two more passes and it goes.
Things we have done.
Changed rigs. All four of ours have worked that stand and all four use the extra.
Checked the boom and the nozzles, because a blocked nozzle gives an uneven pattern and that is exactly what this looks like from the cab. They have been checked every winter and swapped twice.
Changed the approach. I have worked that wing from the other end, from the front, from further out, and with a different spray pressure.
And I have had a colleague stand under the wing with a torch and watch the fluid land, which is not strictly allowed and which we did anyway on a quiet night in 2022.
He said the fluid lands on it. He said it lands on it the same as everywhere else and it beads up and runs off, and the patch is still dull underneath.
The stand.
Stand 9 is a remote stand out on the apron with nothing round it but painted lines and two light masts.
The apron there is the same concrete as the rest, laid in the same programme, and the drainage runs the same way.
I have stood on it in daylight in summer and there is nothing to see. It is a piece of concrete with a number painted on it.
The temperature.
Every rig carries an ambient sensor because the mix depends on it, and there is an airfield sensor at the met station as well.
On stand 9 the rig reads between one and a half and two degrees below the airfield.
That matters more here than in most of these stories, because the mix is chosen from the temperature and a colder reading means a stronger mix, and a stronger mix is more fluid.
But it does not explain four hundred litres, and it does not explain a patch, and it does not explain a patch on one wing.
What I do about it.
I de-ice the aircraft until the wing is clean, which is the job, and I log what I used, which is the record.
I have never once signed an aircraft off with that patch still on it, and I never will, and neither has anybody else on this crew, because that patch is exactly the thing the whole trade exists to remove.
The fluid goes on the bill and the airport passes it to the airline and nobody has ever queried a stand.
The one thing I do that is not procedure is that I take the port wing first on stand 9. You are supposed to work starboard first, because that is the side away from the jetty and it keeps you clear of the ground crew, and on a remote stand there is no jetty and it makes no difference to anybody.
I do it first because I have twice, on a long night, left it until last and come back round to a wing I had cleaned forty minutes earlier, and found the patch back on it, in the same place, the same size, with the rest of the surface still wet and clean and inside its holdover time.