Big Jets - Weather Deviations

[josesilvajs]

Hello guys!

I fly a small business jet (Learjet) and I have a doubt on meteorological deviations for the ones who fly big jets (like the 747 or 777).

In my aircraft, I deviate even from the minor formations, to avoid stress on the airframe and also for the passenger comfort (wich is a great deal in business aviation), not to say to avoid icing.

Do the 747/777 guys deviate as much as we do or their "mighty" aircraft are strong enough to face some mod/sev turbulence with no bad stuf for the passenger and airframe?

Thanks!

[brain fade]

Big jet, wee jet.

Ever seen the size of a Cb?

I deviate for anything I can detect (viz or wx).

I been in a biggy. I not doing it again.:uhoh:

[greenslopes]

When I was a wee laddie wearing shorts, I thought it would be a good idea to press on (C-175), and take the most direct route below a CB. This proved a very bad idea.......Swore that if I got through that I would never go near another one.
Then a few years later whilst operating from Nadzab to Pom entered a CB at night(no Wx radar in a Twotter)............Flight idle FL 150 still going up @ 1500fpm.
Moral is don't go anywhere near the B'strds.
I now fly a nice new smelly NG737 and still don't go anywhere near the mongrels.

[Fly3]

I have operated B744's and A340's in the Pacific and like greenslopes says stay the hell away from them.

[Capt Fathom]

I've also seen a situation where all the big jets were going 150nm off track to get around a line of weather.

The little jets were either climbing over-the-top, or going through the 5nm hole in the middle!

Obviously the owner was not on board, but self-preservation must kick in somewhere? :uhoh:

[The Real Slim Shady]

There is no valid reason to fly through (or very close to) a Cb in peacetime.

[halas]

Last summer a bunch of us were heading west through Romania in clear skies, except for one huge Cb on our track. All the others and ourselves asked for deviations to avoid....except one aircraft.

On the Nav display we watched on the TCAS as he entered the Cb.

His altitude deviations indicated he was having quite a wild ride! The FO and myself watched in total disbelief as he went up and down in excess of 800' within seconds of each altitude deviation. Then he leveled out on the otherside.

He made it, but by :mad: only just!

If you calculated our deviation in miles, it probably added up to what he was doing in feet ;)

halas

[threemiles]

Certainly Bucharest ACC would have warned him/woken him up that others in front of him had deviated. Didn't they?

[Sir Richard]

Similar situation Northbound over southern China from HKG (Kai Tak) to LHR
We deviated about 30 miles off track while the a/c ahead (Also 744 Europe bound) was asked by the ontroller why he had changed his altitude by 300 metres!.....His horizontal deviations were not quite as far as ours !

Cbs are best observed from the outside :}

[Intruder]

fly upwind of the cell at a distance of 1nm per 1knot of actual wind.
This doesn't really make any sense...

With no wind, any hail spewed out of the cloud could go in ANY direction. With a strong wind, it would tend to be blown downwind. Also, in the jet stream you avoid all cells by 100-200 NM upwind? I don't think so...

[Capt Fathom]

1nm per knot of wind?

So what you are saying willnotcomply, if the wind is 60kts, you would divert 60nm to the upwind side of the CB?

[Just another student]

Our ops manual was updated to cover flying with increased CB activity during the summer. Guidlines were introduced, for example min 2000FT verticle clearance, 20nm horizontal on wx radar, 10nm visual and in a TMA 10nm via wx radar and 5nm visual (I believe).

I have seen some BIG ones over Eastern Europe this summer, not when compared to the Asian/USA monsters, but easily FL400. Its amazing how close to these bad boys some people got.

I like to keep my distance from them to say the least :uhoh:

[RMC]

The distance you avoid by is related to height. Typical max distance required is 20 NM...this rule of 1NM / knot is serious overkill (and not practical in an unstable airmass where there are likely to be many CBs within 100nm). I think the original question may be asking about avoidance of Cu and other minor returns from the wx radar. If so the answer is again height dependent. At low levels in a relatively stable airmass there is no need to deviate around a little bit of green at low ranges...its just water! At 41,000 you wouldn't go anywhere near the same return....water has no right to be up that high. Ref also x band wx radar gain bias at short ranges. A small amount of cu (not towering cu) again is unlikely to give more than a few minor bumps at low level...can't complain if someone feels the need to deviate from it for pax comfort but it certainly does not deserve a delay to the approach. This lack of distinction between serious wx and slight nuisance stuff is most often seen in low experience aircrew.

[Dream Land]

"mighty" As far as might goes, the airframe on the LJ is probably much stronger, if I'm wrong I'm sure it will be pointed out to me. :}

[Tmbstory]

CB's

In the 1960's I spent a lot of time cloud seeding in a Cessna 310.

We did two types of seeding, Cu & Stratus, the large Cu was base seeded,(rudder just under the base of the cloud) or seeded at the side of the anvil with a Very Pistol arrangement. The stratus seeding was carried out at OAT -5 centigrade.

The substance was Silver Iodide carried in Acetone. The Acetone was burnt in the discharger & this left the Silver Iodide nuclei in the air. The Silver Iodide nuclei is very close to an ice crystal nuclei & the thinking was that rain would result.

The flying was a great experience & did wonders for your flying skills.

Some spectacular views were to be had.

[SIUYA]

Got to agree with you there RMC.

The commonly-accepted rule to keep your flight from developing into 'thriller' proportions is to avoid by at least 20NM, any thunderstorm that's identified as severe or giving an intense radar echo.

The same avoidance distance should also be applied if you can't clear the top of a known or suspected severe thunderstorm by at least 10,000 feet.

Honeywell agrees with the 20NM avoidance distance, and also provides advice that thunderstorm with tops >35,000 ft should be treated as severe. :ok: