Terrain VS CB

[low n' slow]

Hi all.
I was presented with a little problem last week and I'd like to know how you would've handled it.
The situation was such that we were departing from an airfield with very high terrain around us and the winds were up to 20-30 knots in the gusts. CB's were rolling in from the sea. The FMS SID track would take us straight into one of these. The SID is built like this: Straight ahead to a beacon, when passing 3100 feet, left turn to intercept a QDR from the same beacon and then once on that QDR, slightly right on to another radial. The initial left turn brings us over terrain and the FMS usually flies it all the way to the beacon. Basically it's the pilots decision when to turn left once above 3100 feet.
In hindsight we followed all pertinent limitations regarding terrain clearance and navigational precision, but one thing struck me (and here's my question):
What if the CB had come across our path before the 3100 feet marker on the SID? The left turn would have been illegal in respects to navigational precision. With limited knowledge about the terrain, would you have turned to get away from the CB (away from SID track below turning altitudes, IMC in high terrain below MSA) or would you have continued into the cloud (EMB CB). I was surprised of what my captain suggested but was pleased to see that other commanders had a different view. What would you have done and yes this is basically a question asking "would you choose to fly into a CB or would you go off track, hoping that your situational awareness -in an area in which you rarely fly- was sufficient to keep you from flying into terrain ".

/LnS

[Right Way Up]

Do not takeoff in the first place. If there is weather about I'll try to arrange us to point in our departure direction whilst taxiing so as to get a good look with radar. Failing that have a good look once lined up and if it looks bad taxi off & delay departure. There is no rule that says you must takeoff!

[Bealzebub]

If you are sat on the ground you are safe. When planning a take off and initial departure you should satisfy yourself that it is safe to do so. If the weather by itself or in relation to terrain etc. is giving you serious cause for concern then delay the take off until the situation improves. It is all to easy to fall into the mindset trap of assuming that nothing must delay the flight.

If subsequently the choice is terrain or cloud, pick cloud every time. An encounter with the first will probably kill everybody, the second might provide for an unpleasant ride for a while.

SID,s are just that Standard Instrument departures. They are constructed with regard to many things including terrain clearance, airport arrival and departure flow, noise and other political considerations etc. If the situation is not Standard (with regard to weather) or a departure where visual conditions may better substitute, then liase with ATC and negotiate a safer departure.

There are often occaisions when a compromise has to be made and Captains are normally selected for their demonstrated ability to exercise such judgement. Of course that does not infer that such decisions are universally correct, nor does it infer that they will be made without necessary input and advice from others. However it is important that a timely decision is made.

As regards legalities, rule distances and other perceived violations good planning should normally negate any worries on all of these matters, however where for whatever reason there is a need to compromise then there has to be a simple set of basic rules.

1. Don't risk flying into rocks.
2. Don't risk flying into weather that might damage anybody or anything.
3. If faced with a stark choice between 1 and 2 pick 1.

[low n' slow]

Thanks Bealzebub. I agree with your "simple rulebook".
Inecperience and forgetfulness put us in a cramped position. We solved it all on the safe and legal side but I'm trying to adjust the situation into something where a hard decision needs to be taken. We were unable to check with the WX radar because of all the ground returns (high terrain). It was up to pilot judgement and we decided to go. Anyhow, it was a humbeling experience and I think I've learnt a lot from it.

Right Way Up, you are ofcourse correct in that you do not have to depart if you don't want to. However, it's a big decision to decide not to depart. Not in that it's complicated, but it tends to be quite far from what you were thinking from the start. That said, it is not allways the most obvious solution at the time (although it may well be the best solution). It is often a case of beginning at the bottom and working quickly downwards... What I'm looking for is how to handle such a situation once airborne.

Thanks for your input
/LnS

[Right Way Up]

LnS,
I guess as I get bigger & uglier I find the no-go decisions easier, however as you rightly say once airborne you have to decide quickly the least dangerous option. If I was sure I knew where I was I would risk the early turn, otherwise batten down the hatches. History has shown that granite kills you more often then CBs.
Its a sign of a professional & keen pilot that you question the scenario.

[low n' slow]

Thanks RWU, I try to learn. I wouldn't have wanted to be the guy in the LHS on that flight with my current experience level. The captain of that day is also a very young and very keen pilot and he made an excellent decision based on what we knew then and suggested the left turn. I'm quite shure he at the least spared the company a paint job and certainly spared the passangers some grief. The more I think of it, the more I come to the conclusion that it is all dependant on how confident you are with what the terrain looks like beneath and ahead. High confidence will provide a little leeway with which to compensate for various factors (although my aim will in all normal cases to be bang on ). In this case, yes we were pretty confident.

One suggestion that I got from a more experienced guy was to look at the radar image in clear weather to get a picture of what the terrain will produce on the screen. Then in bad weather, anything in addition to the "normal" picture will be easier to interpret as something to avoid. Will this be useable with regard to the mechanics behind radar? I'll have to have a look next time! Anyhow, I've learnt a lot from this and the subsequent discussion I've had with colleagues and on here.

Thanks/ LnS

[Centaurus]

The other point to keep in mind concerning terrain clearance in IMC if you are in a CB is that pressure variations can cause significant altimeter errors. Very important if you just happen to be obstacle clearance limited with an engine out second or third segment limiting climb. Clearing terrain or obstacle by a theoretical 35 feet is bad enough but with a CB over your planned flight path, it becomes a question of good airmanship or bad...

[low n' slow]

A very valid point Centaurus. Indeed, it is very poor airmanship to depart into a CB as I think I have previously established. Also, with the windspeeds that prevailed that day, one must take into consideration the effects of the terrain aswell as regards to altimeter errors (is it "add 2000' per 20 knots over terrain"?).

/LnS