Flying over fog

LeSving i dont follow your logic. If you selected two different populations, one, let us say where the engines had been blue printed, only the best engineers employed to service and check the engines, and the engines always operated within recommened parameters are you suggesting this populartion would have the same mtbf as a radomn selection?

LeSving wrote:

The MTBF is valid for the straight bottom of the “bath tub curve”. Failures are purely random. There is nothing you can do to improve the failure rate. Even if the MTBF should be 100k hours (more closer to turbine category airplane). One hour over fog would still be about 60 times more risky than one hour in a car.

LeSving I am afraid your statistics is a little lacking. https://en.m.wikipedia.org/wiki/Ecological_fallacy

The average does not describe the shape of the curve or imply a particular outcome for an individual member.

If there is one good thing about the 50-year-old technology that powers most of us along it is that we have a lot of data as to why engines fail.

Yes, there is a random population (I seem to recall as much as about 20%, but can’t find the source right now).
However, as fuji sais there is a lot you can do to keep yourself mostly out of the other 80%:
Ensuring fuel is fed to the engine and generally adhering to known good operating practices
Familiarizing yourself with the aircraft you fly often and it’s engine-related accident/incident history
Using all the early-detection diagnostic tools (compression checks, filter examination, oil analysis, borescope inspections…)
Being on top of your maintenance and knowing engine-related SB’s
…

My view is that there simply are time windows in flying where an engine failure would be death.

One has to keep them as small as possible, or fly a twin, or have a plane with a chute (and then risk getting somebody on the ground if it happens over a city).

Many airports have built-up areas which would make a disaster inevitable, on takeoff or landing.

Then there are the sizeable forests in say Germany. It is virtually certain a plane would be wrecked – some accident reports contain the images e.g. N403HP. Some can get lucky; I knew a group which “landed” a Tripacer on top of a forest canopy in France (flying VFR in ~ OVC002 but that’s another story) and all walked out (of hospital).

The Alps are frequently overcast

but there is a plausible Plan B, with a GPS running a decent topo map.

Very low cloud is common too; this near LFBZ was ~OVC003

So fog is not the biggest fish to fry

Except obviously when arriving or departing, I avoid doing anything to the plane when flying over any of these areas so no fuel tank changes, no power changes.

There is little in the way of engine maintenance that can be done on a Lyco/Conti engine (it is just a sealed lump which you can’t see inside, and generally cannot hear any noises of bearings about to seize up) but you can do

• a good preflight (looking through any openings with a torch; this would have picked up a number of in-flight shutdown cases I’ve heard about, especially one which was never openly posted despite my encouragement involving a hose bracket which broke due to fatigue or rust)
• manage it in flight correctly (with appropriate instrumentation) and watch for anything unusual in the temperatures
• do the 50hr checks diligently, checking for metal in the oil, eyeballing the spark plugs very carefully, checking everything outside, and not allowing defects to be deferred whatever the cost (something not easy when like me you have no hangar where maintenance is permitted!).
• do a good Annual inspection, again not deferring any defects whatever the cost
• avoid “muppet” maintenance and overhauls – this is a big problem in GA, because the whole industry is unavoidably set up to make a living out of the lowest common denominator, so there is an above average % of shysters or simply incompetent people… always get references on anybody you use especially for “mechanical” work, and not use them merely because they post on some forum.

Peter wrote:

My view is that there simply are time windows in flying where an engine failure would be death.

You are right: fog is just one small risk. However engine failure in itself is definitely not the biggest fatality risk in GA.

Mechanical failure (including engine) was involved only in 8% of the fatal accidents in single engine aircraft in 2017 in the US 2017 Nall Report.

Perhaps when flying over fog a bigger risk would be ensuring your destination and/or alternate have good wx, you have good navigation backup and you have plenty of fuel for any reasonable plan.

I quickly recall 8 fixed-wing light GA (non ultralight) accidents just in the Balearic islands in the past 10 years or so:

Two of them were engine failures due to total fuel exhaustion (C172 and PA-34) with no fatalities.
One was engine failure (Airtractor w/ PT-6) due to non-implementation of a manufacturer recommended mod-non fatal
One was VFR into IMC followed by CFIT – Pa-46- fatal
One was performance-related: a max-gross-weight C172 unable to climb in full flap after take-off and stalling – fatal
Accelerated stall-spin in a BE55 at low-level-fatal
Loss of control during landing in a taildragger-I-115-non fatal
Stall-spin during manoueuvring at low-level and low-airspeed-C172- fatal

The geographical proximity of these accidents makes me biased towards not worrying so much about the fog/SEP risk …Of course also being based in Mallorca I worry more about flying over water and address it (other than with maintenance) with raft, lifevests, emergency radio, plb and in-water-training. Coolhand addresses the fog risk with a parachute. Beyond that I place my bets on other risks, the pilot being the top one.

Peter’s idea not to touch anything in those conditions is a good one (if you have enough fuel in the selected tank!)

Indeed; I change tanks at the last possible moment before crossing the area in question, so an engine stoppage due to the tank change would still enable a 180 and a glide somewhere. Even on Shoreham – Le Touquet I do this. The Alps for example are at most 45 mins to cross and in reality less if you are say 5000ft above the terrain so you get 5 mins extra to play with. Fog regions are rarely that big, in terms of a large unbroken coverage with no ground visible anywhere.

It isn’t just fuel. An engine stoppage can happen in IMC at the right temperature and I reckon I could replicate this 100%. You can also do it 100% in a DA42, as one former poster here found out. You just need IMC and -15C. What prevents it is alternate air OR (apparently – hard to prove) prop TKS.

I am the same – but I wonder whether there is any evidence to support this?

In an aircraft without the luxury of a fuel totaliser, and if any where near lower fuel levels, I do make sure there is a fuller tank and switch to the fuller tank before commencing the approach.

Peter wrote:

Fog regions are rarely that big, in terms of a large unbroken coverage with no ground visible anywhere.

Not quite. Try the plains of northern Italy in winter or the Austrian lowlands north of the Alps. You might be surprised….

I wonder whether there is any evidence to support this?

There have been lots of anecdotal reports that a change of power immediately preceeded an engine mechanical failure. It does kind of make sense that the probability would increase. Similarly changing tanks could expose an obstruction. Or it could mask it until you change back to that tank, which is the same result.

It is generally true for mechanical things that they keep running if left alone. Hard disks can run for 10+ years, 24/7 (I have some) but if you turn them on and off daily, no way. Same for electronics (my specialisation); thermal cycling is the #1 killer there, even in “well done” designs. Software is the opposite; needs regular reboots

Try the plains of northern Italy in winter or the Austrian lowlands north of the Alps

I have flown for 5hrs over low cloud, never seeing anything (excruciatingly boring). But not (what I thought was) fog.