Nocturnal Jets

[Pierre Argh]

Perhaps not what you thnk???

Almost 30 years in the ATC game... learnt this one this morning, Nocturnal Jets... never heard of it before?

Big a/c inbound, surface wind calm... quiet, so pilot elects to approach nearest runway but has to break off approach on short finals due to 20kts of tailwind at 200ftAAL???

Met man explains concept: How overnight shallow, but marked, inversion can form over cooling land (typically on long clear Winter nights). Geostrophic wind above inversion layer blows unabated by surface friction causing massive differential in surface wind and wind just above surface (above the Nocturnal Boundary Layer to be precise)...

Figures:
OAT (surf): -4deg SW: Calm
OAT(1000ft): +11deg SW Easterly 35kts

Pilots probably learnt all about that (one way or another)... amazing how much stuff isn't covered in ATC training... or maybe I was asleep at the time?

[brimstone]

Perhaps you were. For precisely this sort of situation the good book says that "when the surface wind is light and variable the 2000ft wind should be taken into account before selecting the runway-in-use." ;)

[Pierre Argh]

Brimstone... thank you, please confirm which "Good book" precisely?

[eastern wiseguy]

CAP 493 SECTION 2 CHAPTER 1

Item 20 Landing direction and runway in use

20.1 "The term runway in use is used to indicate the particular runway or landing direction selected by aerodrome control as the most suitable at any particular time. Normally the runway inuse should be that most closely aligned to the surface wind direction.When the surface wind conditions are light and variable the 2000 feet wind should be taken into account before selecting the runway in use"


Basic MATS 1 .....but you may not be in UK I suppose?

[Pierre Argh]

EW thanks... in this case UK: Yes, but not subject to CAP 493 regs?

Actually the situation was the right runway was in use, but the pilot had elected to fly an approach to the opposite runway in use (possible fooled by the calm surface wind) for expedience... didn't quite work out like that though?