Thunderstorms

[che ci dò che ci dò!]

Hi everyone,

let's say you've to land a medium jet at an airport on which there's a Cb whose base is about 4/5000'. Of course flying an approach beneath a CB is dangerous because of possible windshear, downdrafts, etc, so in such a situation it's wise to delay the approach and in case divert to an other airport with better conditions. If through the Wx radar you see that the CB's dimension are not too big it could be possible to continue the approach because the related weather phenomenons wouldn't be strong enough to endanger the flight. According to your experience what are the cloud's dimenions (in terms of diameter and vertical development) and the related weather phenomenons which can tell you wheather the approach could be safe or not?
I reckon that a CB with a diameter of less than 2/3 miles and a vertical development below 10/12.000' cannot endanger a medium jet. Can anyone say whether this statement is correct or not?

[parabellum]

CB type of weather is usually reasonably fast moving and the active cells usually have some distance between them. Under these circumstances I would advocate holding until the immediate danger has passed and then make your approach. If you do have to make your approach under a cell that has a base of 4 to 5 thousand feet be certain to have the reports from preceding aircraft, as a diversion may be the more prudent course of action. (A CB with a base of 4/5000' is, in my experience, unusually high, 1500' is quite common though).

[SNS3Guppy]

I once rode a microburst down to about 150' AGL beneath what was widespread high bases with a mammus appearance...but no virga, no precip, and no other indications that the downdraft would be present. It was quite a ride.

I've seen thunderstorms that extend only to 12,000' or 15,000 that can put out surprisingly strong downdrafts; don't under-estimate a thunderstorm simply because you think it looks small.

Thunderstorms vary in character from cell to cell, and location to location.

I've seen dry cell storms that can put out severe microbursts with little or no visibile vertical development...cells in the desert which have no visible development, but still create dust-storms from intense microbursts. In some locations (including where I live) I see this regularly at certain times of the year.

Never catch yourself saying "it's just a little thunderstorm." That's somewhat akin to saying "It's just a little gun." No such thing. Thunderstorms can contain forces which far exceed the capabilites of any aircraft, and can and have put airplanes in the ground.

If the cell is moving, let it move then conduct your approach.

[Doors to Automatic]

Never catch yourself saying "it's just a little thunderstorm."

How true - just look at this little beauty:

YouTube - Thunderstorm 9/29/2008 Del Mar, CA (http://www.youtube.com/watch?v=oU_EZ2pPu34)

[411A]

Our ops procedures...
During thunderstorm months (and additionally when they are indicated)...carry an extra hour diversion fuel, subject to Captains decision...
Up to him, all comply, as we employ only experienced folks.
Have there been diversions?
Yes, several. with plenty of fuel for the unexpected.

In reality, there is really no other safe way, especially in Africa, where we mostly fly, on a day to day basis.

Type, Lockheed L1011.

[grizzled]

Che ci do X2,

The report on the Air France accident at Toronto is worth a read. And I second the previous comments: CB's and associated rain, hail, windshear, downbursts etc, are still notoroiusly hard to predict accurately. Discretion, not courage, is called for.

Transportation Safety Board of Canada - AVIATION REPORTS - 2005 - A05H0002 (http://www.tsb.gc.ca/eng/rapports-reports/aviation/2005/a05h0002/a05h0002.asp)