Larry Tuwie has kindly sent me this article on safe altitude and separation. Many thanks Larry I'm sure the visitors to this site will find it interesting.
My instructor was wittering on about something called a flight log sheet which would apparently enable me henceforth to navigate with ease. It might have been something to do with the previous night’s ‘first-solo’ celebration, but it was quite clear to me that this navigation business looked like Bad News. In the quagmire of new data on variation, deviation, RAS, CAS, TAS and groundspeed the column on the log marked ‘MSA’ just didn’t look that impressive - and anyway it was time for coffee.
Several days later the subject of Minimum Safe Altitudes became very impressive indeed, even though by that time I’d already passed the written Nay exam and the Navigation Flight Test. It was time for the qualifying solo cross-country, the weather looked co-operative and we set off in a pair, two Tomahawks with a hopeful PPL aspirant in each.
Guernsey to Nantes was a long but uneventful leg, and I just didn’t believe the French controller when he told me there was “fog” at 4,000 feet! I knew he meant “four octas” and I decided not to ask for French weather on the radio again until my French or their accents had improved. I landed four minutes after the other Tomahawk, and we trotted over to the Met Office and Tower together.
All looked well for stage two to Rennes, so after collecting our certificates proving we’d landed at Nantes satisfactorily we headed northwards. The weather was fine, but we suspected a problem brewing for the eventual return to Guernsey later that day. At Rennes I called the tower first, and was fist on the ground. Again we visited Met together.
Well, hmm, ahh... yes, it looks OK. Certainly for the next few hours, and we won’t need that long. Five octas at 3,000 feet, isolated showers, but we can fly at 2,500 feet can’t we? My previously prepared flight log showed a MSA of 2,000 feet, although basically all the ground for the first half hour out of Rennes was far lower than that. There was just this little radio mast... My ruler had picked this up as being within five nautical miles of planned track at 448 metres amsl, say 1,500 feet. Adding 500 foot clearance from any ‘person, vessel, vehicle or structure’ gave 2,000 feet, so 2,500 feet looked good.
Within five minutes of clearing the circuit at Rennes the “five octas at 3,000 feet in a few hours time” turned out to be seven at 2,000 feet right now. The other Tomahawk was five minutes ahead, and it seemed from his radio calls that he had pushed out through the worst of this unexpected and hopefully isolated occlusion. I didn’t fancy a night back in Rennes, so I followed, getting closer to the lowering cloud base all the while, and only vaguely aware that I was being forced slowly down through 2,000 feet by the dirty wet cotton wool around me.
It seems he was having similar troubles, because just as I was seriously considering a return to Rennes or diversion to Dinard he announced his intention to divert to Dinard. I agreed from the bottom of my heart, said goodbye to Rennes, and leaned over to select Dinard Approach on 120.15.
I was suddenly aware that something other than the radio required my immediate and full attention. I thought I had seen a light in the gloom somewhere ahead, and stared intently through the screen — which was now streaked with rain.
Dead ahead and not far enough below a white strobe suddenly appeared from nowhere. Anti-collision beacon? Where’s the green? Where’s the red? Which way is he going?
(It wasn’t dark yet, but wingtip nav lights when lit give a quick idea of other traffic’s direction, even in murky weather, depending on ‘what’ you can see. My way of remembering which is which is “rEd is lEft wing, gReen is Right wing, on a forward flying plane. So if, for example, I could see a green wingtip nav light on another plane somewhere ahead, I would know he was passing “left to right” – and if it maintained a constant bearing to me, no matter how far away, we’d be on a ‘collision course’ with each other).
It took half a second and one hundred years to realise that “he” wasn’t moving at all, and had other regularly spaced lights strung out directly below, pointing down into the murky gloom. Not a plane: a mast!
Fifteen degrees of bank for a PPL ‘on instruments’ (or nearly so) is a great principle, but that just wasn’t going to do the job, and I had sixty degrees on straight away, my eyes fixed on the black mast now disappearing under the port cowling and still not far enough below. Whether I could see where I was going was no longer the issue; I knew where I didn’t want to go, and I ‘firewalled’ the throttle without delay. I might not be able to see above in the clouds, but at least they’re soft, and that pylon looked very hard.
Recovering my composure I grabbed the map and checked. Yes, it really must have been that mast, and amazingly I was right on track for my diversion to Dinard; but how did I get to be that low? It’s hard to say how close I actually came to it, but if the altimeter had been slightly out, or I’d wrongly converted the metric French maps to feet originally, or I’d ignored my height loss for another few minutes before reaching the pylon, or wrongly set the QNH(altimeter pressure setting) ….
Safely back on the ground during a great meal in Dinard, I had time to reflect on how l came to be there in the first place. I must conclude that the onset of marginal weather is likely to take too much of a basic PPL’s attention, so that somewhat important things can get ignored. On final to Dinard both of us had received a rebuke from the controller with the suggestion that we check the weather before setting off next time. But we had, and I still have somewhere copies of the TAFs and METARs we picked up in Rennes to prove it. The problem is that the weather doesn’t always do as it’s told.
I understand the U.S. Navy published a study showing the average basic PPL has about eight minutes to live in true IMC (Instrument Meteorological Conditions). And although I don’t have an IMC rating (which isn’t recognized anywhere in the world except Britain), here’s what I learned about flying from that incident with the mast:
a) food and beer taste wonderful when you hadn’t expected to be eating again
b) it’s not a good idea to get caught by marginal weather if you’re a basic PPL
c) and if you do, while worrying about everything else and ‘QDMing’ (direction information passed by radio from a ground station) all the way home if you like, watch your altitude above all …