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Notes on accident trends: 2016-2019 BE35

It is commonplace to use an accident per 100,000 flight hours as a metric in GA, and AOPA helps estimate data for the denominator in their GA reports.

http://download.aopa.org/hr/Report_on_General_Aviation_Trends.pdf

The AOPA NTSB search portal allows to drill down by aircraft type, and in this case I selected the BE35. The NTSB mainly gathers USA statistics, but Canada and Brasil seem to be recorded, although not with a narrative.

https://www.aopa.org/asf/ntsb/search_ntsb.cfm

A passenger might be more interested in accidents per departure, and here different types might have more flight cycles as a proportion of flight hours than others.

In arriving at a basis for annual hours and departures for a type, I used an estimate for the type’s active fleet. This is basically a guess based on the production history and reducing the production history by an estimate for destroyed, retired or un airworthy examples. The Beechcraft BE35, (which includes the early Debonair but excludes the E33, F33, G33 and 36 A through G), has had around 10,000 aircraft produced, the last V35B coming off the line in 1982. The G36 still being in production.

Using an educated guess based on active SEP USA fleet trends, I assume that the active BE35 has declined from around 8,000 to 6,000 in the last ten years.

I then used the average SEP annual utilisation and multiplied this to arrive at an estimate for total hours flown by the BE35 active installed base in the USA. This estimates total hours flown starting at around 700,000 and declining to a lower than trend annualised 500,000 hours in 2020.

The BE35 is not used for instruction except for transition and recurrent training. It is also mainly used as a transport. Arguably, departures are a fraction of hours flown. Say around 75%, or average sector is around 1 hour 20 minutes.

Richard Collins helpfully wrote articles on the Cessna 182 vs the 36, one in 2001 which I haven’t been able to track down, with an update in 2016.

https://airfactsjournal.com/2016/11/crash-history-cessna-182-bonanza-36/

Using the fatal accident/100,000 hours metric the 182 was quoted at around .9 and the BE36 at approximately double this, or 1.8.

Am still looking at the data, but an interesting contrast for the BE35 is the near absence of IFR events. This may reflect that the BE35 demographic is mainly using them for VFR flying.

In flight break up, a feature of the type due to its low drag coefficient and relatively neutral lateral stability, read good roll rate, also was not that prevalent.

The total accident rate ranged from 1.7 to 3.6, of which fatal accidents ranged from 19% to 46%. The annual fatal accidents per 100,000 hours ranged from 0.6 to 1.0, which is quite commendable for a 75 year old design.

I was surprised at this rate which does seem better than your average, complex RG. The fatal/total % at around 33% is close to what you would expect from your fixed gear Warrior/Archer/172, which tend to be around 20%, in part due to having a high proportion of instructional hours. An MEP might be expected to be closer to 65%.

Will work (try not to torture) the statistics a bit more, and see what type specific characteristics (eg a fair cluster in poor maintenance, fuel mismanagement and gear up), emerge.

Oxford (EGTK), United Kingdom

Interesting analysis. Are you trying to compare types, rather than type of operation? If so, why not include additional types in the study?
Also, any idea of the potential error in the utilization assumptions extrapolated from the fleet average to a single type? Clearly not all SEP’s are utilized the same 8ie types typically utilized for schools or hire like 172 or PA28 will have higher avg utilization then BE36, right?
Let us know what you find

Antonio
LESB, Spain

@Antonio in the SEP mainstream (excluding Experimental, Bush/STOL, Agricultural, Aerobatic), a priori the world divides between: the simple fixed gear stalwarts (Warrior/Archer, 172 and DA40) with around a 0.5 per 100,000 hours fatal accident rate, and a very good survivability; and the more complex types, with a 1 to 2 rate.

I was surprised that the V-tail had virtually no IFR accident exposure – some night CFIT scenarios, some VFR into IMC, but very few IFR ops. It also had a surprisingly good survivability in some interesting low level manoeuvring and landing accidents. It seems that the V-tail has gone from being a professional/entrepreneur personal transport, to a mainly airline/commercial retiree market, with a shift in riskiness of operations: mainly pleasure flying by well rated pilots.

I will have a look at the 210 and BE36 segment for similar years and see what comes up.

Will also run a Poisson distribution on some of the statistics, to see what confidence ranges emerge. Like the Number 6 bus, you might wait for many months before you get a fatal/serious accident, and then three or four turn up in a month. While I enjoy Richard Collins’ writing, his use of a single statistic, the fatal accident/100,000 hours is not that interesting statistically.

Note the active fleet of these types, the 210 and BE36 is smaller than the V-tail. A proportion of them are still operated commercially as cheque/cargo/bush aircraft. A priori I also expect to find more IFR exposure.

Oxford (EGTK), United Kingdom

@Antonio have had a look at C210 records for the last 5 years. It picks up some T210, but I expect the P210 needs a separate filter.

The last 5 years is more like 4 years due to 2020. Have estimated fleet hours and departures as before.

Both types do not exhibit what a more qualified statistician might describe as stationary Poissonic distribution, but for different reasons. (Ed. sounds like something Freudian).

Around 17% of the BE35 accidents were due to fuel mis management/exhaustion in the 2016-2020. Around 25% of the C210 accidents were due to landing gear malfunction/gear collapse/gear up.

Like the BE35 there was hardly any IFR accidents, only one due to engine failure.

In the period there were CE210 45 accidents, of which 14 were fatal. As a proportion similar to the Bo but with more variability. Nearly half the fatal were in Latin America, where the 210 is much prized for its ‘load carrying’ and ability to use relatively unimproved strips. Adjusting fleet time for the Latin America over representation in fatal accidents, the 210 has a pretty good record, and I estimate a slightly lower fatal rate per departures or 100k hours than the BE35.

Both types are running around 0.7 to 1.5 fatal/100k hours depending on the accident year. Using a poissonic confidence interval it doesn’t preclude that in a given year or month you might not get a Number 6 bus effect, and four or five come at once.

What I found very interesting is the lack of hard IFR events for these serious piston tourers. There was the expected small number of VFR into IMC accidents by non IR qualified pilots, especially at night (some due to spatial dis orientation), but 90% of accidents were VFR in VMC. The positive way to interpret this is that these are by the numbers IFR aircraft, and if flown accordingly on IFR flight plans, the accident record is excellent.

The proportion of maintenance or post maintenance events was expected, and the sixty plus year old airframes (now worth in some cases less than half the price of an Archer) are not getting the TLC they require. Arguably the Beechcraft maintenance schedule requirements is weeding out old airframes that are not being maintained correctly better than the Cessna regime.

If you filter for the post V35B and post 210L models the engine and maintenance related events improve.

Oxford (EGTK), United Kingdom

I wonder why different types show different accident rates despite apparently being used for the same mission profile.

Could it be some subtle (or not so subtle) marketing difference which selects different types of pilot personality?

Administrator
Shoreham EGKA, United Kingdom

@Peter looking at the C210 and the V35, statistically they are very similar, except for some type specific system clusters. They also share Continental power plants. There isn’t a statistical difference in my view, and better than I expected.

The V35 is ‘sexier’, although the 210 is a burlier haul carrier. The V35 landing gear gives it back country cred, and both the A36 (Bonanza landing gear and cargo doors) and the 210 are used in commercial ops in gravel/dirt runway conditions. Both types had landing accidents (excursions or overruns) which may reflect tarmac pilots testing their backcountry limits.

They both had instructional accidents with pilots converting on type. Both aircraft are pretty vice less, although the sportier V35 has more neutral lateral stability (better roll rate) so can head towards a spiral descent quicker than the more rock like 210.

Oxford (EGTK), United Kingdom
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