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Singles versus Twins

From another forum: 93% of non commercial accidents are in singles, 7% are in twins. The FAA says that singles are flown 12.16 million hours per year and twins are flown 1.82 million hours per year in the US. That means that singles have twice as many accidents per flying hours as twins.

Wherever that figure that we’ve heard bandied around for the last decades comes from, I don’t know, but they’re not true according to these documents:



Not surprising, single engine fixed gears have the highest accident rate, followed by retractables. Safest of the singles are the turbines, but they’re not safer than turbine twins.

Last Edited by AdamFrisch at 04 Jan 04:25

These figures are probably right, but still most accidents in single have less dramatic consequences than the ones in twins with their higher mass and speeds.

This needs to be screened for fatalities. As Alexis indicates higher kinetic energy a priori will penalise survivability on the typical MEP with a fibreglass nose as your crash structure.

Oxford (EGTK), United Kingdom

There is no right answer to this question. Twins address mechanical failure risks and other than during takeoff are safer in that respect. Pilot error is arguably more dangerous in a twin. But as with all these things there is so much idiosyncratic component to the risk that I am not sure macro level statistics help much.

And every debate degrades into twin pilots arguing they are safer and single pilots doing the same for their aircraft.

EGTK Oxford

Generally MEP flown to CAT performance conditions should be safer. So if private ops are flown to commercial SOPs this thesis should hold. Statistics suggest that this does not occur.

Oxford (EGTK), United Kingdom

I think that with MEP it is more a case of pilot proficiency particularly in respect of asymmetric flight. I remember when I was training for my MEP on my last training flight before the test I had a new instructor because my normal one was busy. As we approached for the final landing at decision height he asked my to go around – he had actually turned off the fuel supply to the right engine without me noticing – hard to recognise an engine failure at that point – as I completed the base turn and when I put on full power you can imagine what happened! A good lesson in asymmetric flight although I scared the controllers in the tower as I veered off towards them!

EGBW, United Kingdom

Statistics suggest that this does not occur.

The problem is that these statistics are derived from a very small number of samples and therefore don’t have much scientific value. The usual categories of accidents happening to light aircraft (e.g. loss of control when entering IMC, forced landing after engine failure, …) probably only have one or two entries each for twins every year, which is insufficient for a statistical evaluation. Additionally, twins are usually flown by a different kind of pilots with a different level of experience and different flying profile compared to those who fly singles. So this is really a comparison of apples against pears!

EDDS - Stuttgart

You can still use the experience of 60 years accident statistics combined with common sense assessment of pilot currency/proficiency/qualification to risk assess whether as a passenger you have a higher or lower risk of morbidity/mortality. Mission profile and concepts drawn from ALAR would further refine this, and I would suggest would prove useful in helping you decide the riskiness of getting aboard.

Oxford (EGTK), United Kingdom

single engine fixed gears have the highest accident rate, followed by retractables

Isn’t that just down to the number of fixed SEP’s flying compared to retractable SEP’s?

…and I would suggest would prove useful in helping you decide the riskiness of getting aboard.

I’m still not convinced. I’ve been around aviation for 30 of the 60 years you quote, both as a theoretician and a pilot, and I would not be able to assess my risks when boarding a light aeroplane. Far too many unknowns in the equation. The population of aircraft has changed significantly over the last 30 years. There are quite a few modern singles on the market, some even with modern engines, whereas most piston twins are now over thirty years old. Therefore I think we can forget all statistical data that is older than 10 years or so. Not relevant for today’s pilots and aeroplanes. One example (can talk for my part of the world only): In the past, there have seen very few training accidents in light twins. Multi engine instructors needed to be experienced and therefore knew what they were doing and knew what to teach their trainees. Now we have a lot of training accidents (two Vmca demonstration crashes with german registered planes alone in two years). I think because eveybody who has completed an integrated ATPL course and an instructor course can be a multi engine instructor now. With something like 30 hours of MEP time in his book, none of them without his own instructor on board. What level of competence can these people teach their students? Catastrophically poor training together with an aging fleet of aircraft that are more and more expensive to operate and therefore fly less and less will lead to a totally different kind of accident statistic than that of 30 or 60 years ago. Impossible to compare.

EDDS - Stuttgart
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