In a SEP, not being able to land straight ahead is the main issue. This can happen in non-zero vis, if the terrain around has no fields, but remember the loss of power may happen a little later, and you may be able to turn back or find a road nearby. With zero ceilings, you have no chance. The situation is similar to low-speed low-altitude overflight of inhospitable terrain, but even worse (because you can’t even aim for the least dangerous visible option or reduce speed before impact).
In a MEP, it’s similar in risk probability to losing all power when overflying large bodies of water, but the severity of the outcome is much worse (crashing in terrain vs ditching), and the only additional equipment that can help you is CAPS – IF you’re high enough to deploy it.
maxbc wrote:
The situation is similar to low-speed low-altitude overflight of inhospitable terrain, but even worse (because you can’t even aim for the least dangerous visible option or reduce speed before impact).
I agree, which makes it similar to night flight as well. The risk in case of power loss in unquestionably higher. I guess my point is that the risk is a calculated one if you have a well-maintained aircraft and sufficient fuel.
You are of course right that the risk is a calculated one. But wouldn’t it be much less of a risk to make an LVTO a “no go” for an hour or 2 especially as most of us are flying ga for pleasure. It wouldn’t make you a wimp, despite what some pilots might think.
gallois wrote:
But wouldn’t it be much less of a risk to make an LVTO a “no go” for an hour or 2
What do you mean exactly by making it a no go “for an hour or 2”? You mean waiting an hour or two to see if the RVR improves?
boscomantico wrote:
I find it incredible that that book, which as we can see is used a lot by IR students, says that for non-commercial operations, RVRs of 0 are permissible.
@ch.ess yes that’s the paragraph I was referring to.
I’m just preparing stuff to have the right answers. This and e.g. also the missing requirement for having an alternate when the weather is forecasted good enough at the destination are among those things that I could imagine to be topics of “pilots talk” for an exam. Normally you get judged whether the right mindset is present.
gallois wrote:
You are of course right that the risk is a calculated one. But wouldn’t it be much less of a risk to make an LVTO a “no go” for an hour or 2 especially as most of us are flying ga for pleasure. It wouldn’t make you a wimp, despite what some pilots might think.
If you mean what dutch_flyer thinks, then no. It wouldn’t make it much less of a risk. The additional exposure time for a LVTO compared to unlimited visibility below clouds with a cloud base of 200’ (say) is measured in seconds.
I find in many parts of France especially Brittany and Western France all the way down to the Pyrrenees and Spain, the weather changes quickly. It’s not unknown to have thick fog covering the aerodrome.and a couple of hours later gin clear skies. I never allow myself to be that pressed for time that I need to take off when I can’t see the prop. I fly for fun and so I limit my exposure to risk where possible.
In a MEP, it’s similar in risk probability to losing all power when overflying large bodies of water, but the severity of the outcome is much worse (crashing in terrain vs ditching), and the only additional equipment that can help you is CAPS – IF you’re high enough to deploy it.
I don’t understand this. Is it comparing SEP losing engine at takeoff in fog with MEP losing all engines over water? Or I didn’t get it correctly?
No. I was trying to re-map the risks to “known” situations in order for each to better evaluate the risk they are ready to accept. I made a comparison in the SEP case (comparing zero-zero takeoff to another “known” risk situation) and a separate comparison for the MEP case.
In a SEP, if you lose power after takeoff in zero-zero, it’s a very bad day. We train heavily for engine failure after takeoff, this has a real chance of happening at some point in your career. So the risk is equivalent to taking the risk of engine failure after takeoff and making it basically lethal.
In a MEP, the main risk I’m considering (there are obviously others) is the risk of losing climb / level flight at low altitude.
Losing the ability to fly level is similar in probability to ditching in the North Sea for instance. Compared to ditching, you’re less likely to run out of fuel (maybe…), but put more stress on the engines (takeoff power). I admit this reasoning is a bit shaky, but the ballpark comparison is about correct. So the risk (of catastrophic IMC crash at takeoff) is comparable to the risk of ditching in general, but again making it much more deadly. It sure doesn’t look as bad from this point of view (you zero-zero takeoff maybe just once, and ditching is not that common in MEP), but remember we also have a lot of safety gear to mitigate the lethality of a ditching (raft, dry suits etc.), so the probability cannot be THAT low.
Then to everyone their own decision, based on the situation and what they are ready to accept. I know based on these comparisons I would probably not do a SEP zero-zero takeoff if the layer is horizontally extended, and 200ft thick or more (because then, engine failure after takeoff is basically lethal).
maxbc wrote:
Then to everyone their own decision, based on the situation and what they are ready to accept. I know based on these comparisons I would probably not do a SEP zero-zero takeoff if the layer is horizontally extended, and 200ft thick or more (because then, engine failure after takeoff is basically lethal).
How does the thickness of the layer matter?
Would you do a takeoff if the viz was 10 km and the cloud base 100 ft? 200? 500?
