"Caution rotor downwash"

[tmmorris]

How much should that worry me?

Cleared for takeoff yesterday at an RAF base in the south of England... Two Merlins in formation taking off ahead, 'Clear take off. Caution rotor downwash'.

Do the same rules apply as for wake vortex, i.e. take off before their lift point, keep above? Hard to do if they take off aggressively and I'm in a 152...

Do the vortices travel down and outwards? Presumably they drift downwind?

Tim

[M609]

If you departed in a C152 behind one or more Melins, I would have to use 2 minutes wake turb spacing assuming same departure position. (actually, we class all light/medium helos as "medium" in relation to light aircraft)

Don't know if the RAF use WT seperation.

Rotorwash do travel down and out, and affect other aircraft quite simmilar to wingtip wake. It does drift downwind, but I belive at a slower rate then normal wake.

[High Wing Drifter]

A Merlin! I bricked myself getting caught in an R22's rotor wash at Blackbushe. That's is at least one mistake I won't be repeating :oh:

[Cool_Hand]

Last summer I was landing at Blackbushe and there was a helicopter (Dauphin sized) hovering off to the side of the runway not quite level with the threshold. I saw it and thought that it was far enough away that the wash wouldn't really be an issue. As I was crossing the threshold just before flaring the rotor wash pulled me straight towards the ground from about 10' up, I reacted quick enough not to cause any damage but had the stall warning going throughout.

Afterwards I went and looked up rotor down wash patterns and strength on the internet and found some interesting articles, which agree with M609. The outcome is, it does travel downwards and out up to I think it said about 10 times the rotor diameter, with it being stongest in the hover. They also tend to hang around longer

I would apply the usual rules for avoidance if possible or delay departure/arrival for a suitable time.

I've also experienced wake turbulence, the rotor wash was significantly stronger

I am now very aware of helicopters operating anywhere near me.

[jayteeto]

I would be very careful. Not sure on the details, but wasn't there an accident at St Mawgan recently in similar circumstances??

[Spitoon]

Speaking as a controller, my experience would suggest that wake turbulence from helis can be significant (and a significant hazard to light aircraft). AIC 17/1999 (Pink 188) gives a bit of info that might be useful but the diagram would appear to show vortices in flight - I think the effect of heli vortices in low level hover or at lift may be substantially greater.

I remember that there was an accident at Oxford a few years ago. IIRC an aircraft (PA28?) touched down adjacent to a S61 at the holding point and the pilot of the aeroplane was thought to have lost control because of downwash from the rotors.

[M609]

Nearly 2 years ago (before we got a badly needed update of our WT rules), I got to see what the wake of a Sea King HC.4 does to light aircraft. The SK departed on the paralell TWY (close to the runway) and a Grob 115D made a TGL on the runway 1 minute later.

The Grob rolled aprox 45 degrees right (away from the TWY) when at 50ft, and was "lifted" 100 meters in the same direction horisontally.
Scary, especially since there is woods and a HAS farm on that side of the runway.......... :ugh: :ugh:

Today the controller that was working then, agree that the rules update was badly needed as well :E

(We needed to apply WT sep between departures, but not departures and TGL when VFR, only to caution. Scary!)

[Obs cop]

Many years ago, one of the pilots on 750 squadron at Culdrose (where I was a stude at the time) had a scary moment during their trappers ride.

If my memory serves me correctly

Practicing a single engine asymetric approach on rwy 30 the Jetstream descended towards the runway, where it then came across the downwash of a Seaking hovering on the upwind side of the runway. The downwas rolled the jetstream rapidly towards the dead engine and the pilot only just managed to recover it from the ever increasing bank angle despite full left aileron.

The downwash from 2 merlins is just a scary thought, especially in alight aircraft.:eek:

Obs cop

[niknak]

Vortex wake from a helicopter is the same vortex wake from a fixed wing as far as ATC is concerned.
Vortex wake between departing aircraft must be applied by ATC, no excuses anywhere along the line.

I would estimate that a Merlin is a "small" wake vortex category aircraft, and therefore the ATC unit should have applied a minimum of 2 minutes between their departure and yours.

However, as it was a military ATC unit, it's not entirely suprising that they didn't have any appreciation of the consequences... :rolleyes:

[Squadgy]

I'm constantly reminding fixed wing and light heli traffic of the risk of rotor wash when FISOing, alsthough we can't delay traffic for it - we have a based MD902 who occasionally departs/ lands along the active runway and even the odd Puma and Merlin- we warn the departing or landing traffic 'caution rotor wash' - most take the hint and wait a minute or so, although a few don't - have seen a couple of Cessnas nearly come a croppa !

[MichaelJP59]

we warn the departing or landing traffic 'caution rotor wash' - most take the hint and wait a minute or so, although a few don't

Would it be against the rules to add "caution rotor wash - recommend 2 minute hold"? Might help, especially if it's a low hour pilot (like me)!

- Michael

[Pronto]

Let's not forget the effect of rotor downwash on bystanders (or pax) too. First time I ever went on a Chinook we boarded via the rear ramp with the rotors turning. I was carrying a Bergan (as we all were). The "sail effect" provided by the Bergan, once I got under the rotor disc, nearly took me off my feet.

There's a lesson there, but I'll leave it to others to tease it out.

P

[Squadgy]

Would it be against the rules to add "caution rotor wash - recommend 2 minute hold"? Might help, especially if it's a low hour pilot (like me)!


It might be legally possible - would be a question for SRG. Consider though that if we have say five aircraft in the cct and we warn someone and recommend a two min delay - we would then have cct traffic reaching final with the departure sat on the runway, as we can't tell aircraft to orbit/ extend downwind etc to fit in with what's happening on the runway. This would increase the number of go-arounds.
It's not really too much of an issue anyway as most of our helicopters don't join to the active.

[FWA NATCA]

If you want to receive a good lesson about helicopter rotor wash ask your local military helicopter unit to put on a demostration where they use smoke to show how far out rotor wash looks like and the distance that it travels from the helicopter. The larger the helicopter the more dramatic the demostration is.

We use to do this at least several times a year for the local college so that they would learn to respect the rotor wash from helicopters.

Mike

[Croqueteer]

:ooh:
Many years ago at ABZ on short finals with a fully laden Viscount I flew through the wake of S61 that had just touched down on a cross runway, and was rolled to at least 45 degrees before I could catch it. As a few have said, be very wary of chopper wakes.

[M609]

To get a 412SP to make low hover down a runway covered with 4 inches of dry snow allso does the trick as demo of wake to trainees. :p