Risk Considerations - Big Aeroplane/Little Aeroplane

[john_tullamarine]

A thread in the Dunnunda Forum raised the old hoary concern, in relation to safety standards in closed charter operations, of "if it ain't big, it ain't good".

As

(a) this has long been a festering point of discussion and argument, and the answers are not at all simple or easily determined

(b) the end user/management chappie who pays the service provider often is not well educated on the ins and outs of the problems and the sort of decision models he/she ought to use in determining where and how the dollar is spent

(c) PPRuNe members will have, in toto, a vast accumulation of experience and knowledge in the realm of fly in fly out styles of operation .. and, no doubt, a wealth of directly relevant anecdotal tales

... might this not be a suitable forum to investigate some of the pros and cons, difficulties, etc .. associated with operations of one class of aeroplane (or helicopter) when compared to another.

My intention is not to generate a tit for tat oneupmanship thread .. that is a pointless exercise .. rather to investigate, in a serious and rational way, some of the problems involved in balancing costs, operational feasibility, and end customer perception .. against the difficult realities of providing a closed shop charter air service typical of what one sees in mining FIFO, government transport requirements, etc ... considering that very few organisations have unlimited dollar resources .. so hard decisions, involving costs and other tradeoffs, have to be made.

More importantly ... for each problem which might be raised .. there will be a range of reasonable options with which the problem might be controlled or contained .. it is this sort of discussion which might prove both interesting and valuable ..

At long last .. I have eventually started a thread ...

[gaunty]

I'm up for it

I'm actually in the middle of completing a little essay for a Coronial on this very subject.

Most of the decisions are being made in a vacuum of knowledge by all the participants, including surprisingly or not, the operators offering the service.

Heres a starter;

Are some of the miners now using FAR25 30 seat aircraft because the seat cost against using 3 x 10 seat FAR23 aircraft to just happens be "cheaper" and/or more convenient, or is the underlying driver the FAR 25 protection and would he know the difference.?

Does he think he is safer because it is bigger rather than as a deliberate certification issue.

If size is the criterion, does the punter see a Beech1900D as "better"/"safer" than say a Citation 500.?


Give me a day to clear the desk, so to speak and I'm up for it.

[Genghis the Engineer]

CAP 701 gives the following values for UK registered aircraft in the period 1990-1999...

Airlines, above 5,700 kg MTOW: 706 million flights, no fatalities, 24 accidents with 91 injuries, 108 accidents without injuries. Passenger serious injury rate 1 per 118 million.

Airlines, below 5,700 kg MTOW: 3.3m flights, 3 accidents with 15 fatalities, 5 injuries, 5 accidents without injuries. Passenger fatality rate, 1 per 220,000.

Air taxi, no fatalities or injuries in 0.8 million flights, 10 accidents without injuries.

Public transport helicopters, 18 million flights, 3 accidents with 18 fatalities+5 serious injuries+7minor injuries, 3 accidents with 3 serious injuries+4 minor injuries, 13 accidents without injuries. Passenger fatality rate estimated at 1 per 1m.

Public transport balloons, 0.6m flights, 1 accident with 1 fatality+7 serious injuries + 4 minor injuries; 30 accidents with 23 serious injuries and 49 minor injuries; 9 accidents without injuries. Passenger fatality rate 1 per 0.6m.


So there does seem a fairly clear trend that part 25 aeroplanes offer far lower risk than part 23 aeroplanes. I confess that I'm surprised to see that helicopters come out safer than smaller airline operations.


To put it all in context, the fatal accident rates for GA in the UK are:-

certified FW: 1 per 71,500 hrs
certified RW: 1 per 53,000 hrs
Gliders: 1 per 47,000 hrs
Microlights: 1 per 50,000 hrs
Gyroplanes: 1 per 8,000 hrs.


G

[Captain Stable]

Genghis, for those who are unfamiliar with FARs, could you provide a brief outline of the differences in aircraft certification categories?

[Genghis the Engineer]

The big difference in FW certification is between parts 23 and 25.

FAR=American code
JAR=European code

Part 23 (either FAR or JAR) is for a/c up to 5670kg (12500lb) carry up to 9 pax, or for twin-prop a/c up to 8618kg (19000lb) carrying up to 19 pax. FAR-23 also allows 3+engined aircraft, such as the Trislander. For any part 23 aeroplane, Vso must not exceed 61 kn CAS.

Part 25 covers anything bigger, faster or more complex than this definition.

In the UK and Europe we have a couple of smaller aeroplane codes. These are:-

JAR-VLA, non-aerobatic 2-seaters up to 750kg MTOW
JAR-22, gliders and motorgliders up to 850kg MTOW

These I think with a bit of haggling are generally also accepted by the FAA as an acceptable alternative to FAR-23 for aircraft in these brackets.

There are also two national only microlight codes (that is single seaters up to 300kg or 2-seaters up to 450kg), which are BCAR Section S in the UK, or BFU-95 in Germany. Many countries will accept either or both of these codes for aircraft in the microlight bracket.

On the rotorcraft side, part 27 covers small rotorcraft (up to 2727kg / 6000 lb) and part 29 large rotorcraft.

Less well know is FAR-31 (Manned Free Balloons), and it's UK counterpart BCAR-31


All the way along, what you find working with them, is that the bigger and heavier an aircraft is, the more stringent (and expensive) certification is. That's why so many twin-props have exactly 20 seats or smaller aircraft exactly 10 seats, adding 2 seats to a 10 seater probably doubles the certification cost. It also goes at-least part of the way to explaining why bigger heavier aircraft tend to be safer.

G

[gaunty]

Below an excerpt from a little exercise I have just completed for some what are quaintly termed lay persons, in a attempt to describe some of the esoterica.

The TWO basic categories and rules are those described in FAR Part 23 “Normal” and FAR Part 25 “Transport” for the design manufacture and certification of aircraft for their intended use.

The two Parts, 23 and 25, are separated historically by, or the distinction made between the two categories, as a maximum take off weight limit 12,500lbs (5700kgs), FAR Part 23 being less than and FAR Part 25 more than 12,500 lbs (5700kgs)

The significance of that particular weight as a determination surrounds the generally accepted definition of what was then, in the DC2-3 days, an “airliner” used for the carriage of the public as fare paying passengers on Regular Public Transport flights (RPT).
It marked the commonly accepted distinction between small and large in size and passenger capacity

The intention was to formalise a distinction between aircraft construction, design and safety provisions between what was considered acceptable for private business and recreational use (assumed to be informed use) and a higher and more robust level of safety for the public (individuals protected by Government license and regulated) use on RPT.

Up until then design and construction for all uses was pretty well based on what could now be called FAR Part 23 “Normal” category, within the limitations of the engines and technology then available.

The industry recognised that if aviation as a routine form of public transport was to be made as safe as possible and taken beyond the “novelty user”, a more rigorous standard than that extant would be required and that there was now sufficient experience for this to be formulated in a rational manner. The evolution of the turbine engine with its high power to weight ratio allowed the full development of the concept.
The basic underlying concept to FAR Part 25 has always been to provide the highest level of redundancy possible and reduce the risk to the fare-paying passenger from any event or combination of events to a very low level of probability within the bounds of the available technology. FAR Part 23 for some of the reasons stated below is much less rigorous.

APPENDIX “A” attached presents a simplified table of the differences between the FARs Part 23 and 25, and as a reference to the ensuing discussion, it is by no means exhaustive but serves to make the point.
APPENDIX “B” attached contains a short description of the FAA FAR Parts 23 and 25. The full text is available at FAA Federal Aviation Regulations.

It was also recognised that a distinction was necessary due to the significant difference in cost of purchase and operation between the two requirements resulting from the extra weight of airframe, systems, bigger power plants (the rules effectively require 2 engines as a minimum), higher performance, avionics and flight crew to meet the higher structural integrity requirements, system redundancies, more powerful engines for performance, sophisticated avionics and navigation equipment and number of flight crew required to operate the more complex aircraft.

It was not considered “fair” to burden the private operators with the significant extra costs of a “public” requirement that they, the private operators, could not defray by selling seats in an “airline” operation.

Hence the core basic regulation “FAR Part 23 Normal, utility, acrobatic, and commuter category airplanes” was reserved to private operations. It should be noted at this point that the inclusion of the “commuter” category within FAR Part 23 did not take place until later for reasons I will describe shortly.

So we now have the situation that a regulatory “distinction” based on a philosophy designed to further protect the public that was valid in the thirties of the last century but has not been so since, in my opinion, at least the late sixties, has become enshrined in the law and has skewed the evolution of aviation particularly in Australia to this date.

It has encouraged the use of aircraft for purposes for which they were not originally intended.

The Australian and other regulators have imposed certain layers of “extra compliance” on top of FAR Part 23 operations in certain commuter and Instrument Meteorological Conditions in an attempt to emulate the higher standard required of FAR Part 25 operations where the FAR Part 23 type aircraft is used in “public” operations, but it if not fundamentally possible as a result of the PART 23 design and performance requirements to reproduce anything like the same result.

The US FAA found it necessary to promulgate a “Special” FAR Part 23 (SFAR Part 23) “commuter” category to fill a gap between FAR Part 23 and FAR Part25 aircraft , which goes some of, but not all of the way.
The SFAR23 is an attempt to accommodate a “crossover” in size, performance and cost, between the smaller nine (9) passenger FAR Part 23 types used in charter and in short distance, low volume commuter RPT runs to remote or small communities unable to support a FAR Part 25 aircraft, and a bigger stretched King Air 200/Beech 1900D, 19 seat (by regulation) FAR Part 23 type aircraft that “falls” over the pre-war arbitrary weight divide This type has a MTOW of (16,950lbs/7704kgs) that demands FAR Part25 design, but which for reasons purely economic were exempted.
The determination of the “exemptions” to the surrounding philosophy and law seemed to surround a opportunistic upgrade of requirements around what was possible within the FAR Part 23 framework and limiting the number of RPT passengers (to 19) exposed therefore to the lower “level” of safety actually required for RPT by FAR Part 25.

I do not recall there ever being an informed public debate on this “exemption” and certainly not within this country.
The “differences” or “distinction” between FAR PART 23 and 25 is not well understood, in some parts not at all, in the industry or even at the regulatory level on the ground. To date the industry has become almost entirely driven by regulation applying the application of certain standards to aircraft of each category (FAR PART 23/25) without a fundamental understanding of the underlying philosophy.

There are some important and fundamental philosophical differences betwen the two Parts.

I tried to import the Table of differences but the formatting wont translate. When I get a moment I'll try to break it down so it will translate here.
Here is a good place to start your own research

Federal Aviation Regulation Parts 23 and 25 (http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfrv1_00.html)

[john_tullamarine]

Gaunty hits the main problem nail on the head ...

"Most of the decisions are being made in a vacuum of knowledge by all the participants, including surprisingly or not, the operators offering the service"

and this was my reason for starting the thread ...


Genghis then gives some of the typical historical accident-related stats which go some of the way to indicating that there is a wide range of "safety" outcomes .. "safety", in this sort of discussion, really is the inverse of risk .. ie high safety follows from low risk (or, if you like, high priority attention to sound risk management). I suggest though, that it is not just a matter of the certification of the aircraft which is relevant .. but many other factors .. including, for instance ..

(a) geographical and environmental areas of operation
(b) crew standards, experience, and training
(c) maintenance
(d) level of support services, both internal to the operator and customer .. as well as external (weather forecasting, regulatory requirements, manufacturer support etc etc ... )
(e) operator and customer management attitude and SOPs

etc etc etc ...

Genghis and Gaunty then gave a good rundown on some of the certification details. If I may be permitted to paraphrase and cut to the quick, what it comes down to in this area (ie regulatory) is something along the lines of ...

Looking at it historically (and, if anyone is interested, we can probably dig out the dates when the various changes came in .. on that topic, the FAA website permits the building of superseded sets of US regs .. very useful tool)

In the beginning (as in early 20th century) a bunch of rules had to be made up to try and impose some control on a burgeoning new industry .. and, looking at some of the US tales I have heard from the very early days, there was some head scratching and reasonable positions taken .. eg Genghis notes above that the max stall speed for a single is 61 kt .. which is the equivalent of the earlier 70 mph ..which was dreamt up in the early days as being a finger in the wind speed at which a controlled crash landing ought to give the occupants some unspecified, but well-intended, measure of survivability.

The rules then diverged into specific sets for

(a) big aircraft (typically DC3 and up)
(b) little aircraft (typically ragbag machines .. Austers, Cubs, etc)

The 12500lb, if you look at the weights involved, happened to be near enough in the middle of no-man's land and was picked as a figure which wouldn't cause anybody any angst.

This all went along nicely, until the advent of little turbines permitted the small fraternity to nudge 12500 lb. Naturally enough the manufacturers lobbied to have exemptions granted to permit progressive encroachment above the magic limit.

After some years of, perhaps ill-conceived and unfortunate growth, the regs were updated to include these middle range commuter aircraft. In recent years, additional standards have sought to address the low end recreational aircraft market.

The basic design standards philosophy for the "serious" aircraft was to improve the regulatory requirements, more or less constantly, in line with realistically achievable technology. So, for just one instance, we have seen the development of dynamic seat crashworthiness and improved interior flammability requirements.

In simple terms, what it comes down to is this ...

FAR 25 (for FW) and FAR 29 (RW), and the JAR equivalents, in association with the operational standards, seek to impose a high level of systems (used in its widest meaning) redundancy and a high probability that a given flight might be terminated satisfactorily in the event of a significant malfunction. Note that I don't use any terms which might infer a guarantee .. there are no guarantees .. only probabilities (or risk levels) .. for which defined minimum standards are specified .. and for which sensible in service risk management programs can further enhance the "safety" of the operation. Furthermore, any aircraft, including the latest FAR 25 compliant designs, can quite easily find conditions where it is all going to turn pear shaped ... extreme windshear, significant multiple system failures .. etc

Do keep in mind, though, that the FAR 25 of some years ago is a very different animal to that which you can read about on the FAA website .. an older design will, necessarily, be less well endowed than the very latest design.

FAR 23/27 provide a reasonable standard for smaller machines used for essentially recreational and business activities. It follows, then, that additional airworthiness and operational standards need to be applied if this category of aircraft is to be used in scheduled or charter operations which demand a lower risk scenario.

It also follows that the end customer, in the closed shop charter arena, and the operator as well, can impose further risk lowering requirements .. multi crew in lieu of single pilot, additional equipment, restrictions on operations, etc. The worry is that this is often done in a well-meaning, but ineffective, way. For example, just to put a second pilot in the RHS .. doesn't necessarily help the situation at all .. unless sensible training programs are required as well ..

The Commuter category requirements seek to improve on the FAR23/27 world to go some of the way toward making those bigger little aircraft, which Joe Public presumes are the same as the big aircraft, possess lower risk in operations than they might otherwise have.

It is very important to remember that the airworthiness design standards (FAR 23/25 and the like) do not address operational matters to any significant extent and one has to look to the operational standards (FAR 91/121/135 etc) to fill in the gaps and find a reasonable whole.



That's all fine ...


But, at the end of the day, dollars and practical reality are important.

Often, the big aircraft cannot be used, either due to physical constraints (the strip is too small, the approach too tight, etc), or straight economics (the seat-mile cost is too great for the project to sustain, etc)

So, what do we do ?

(a) just bury our heads in the sand and say it's all too hard ? Maybe you can do the trip some other way. Let me give an example of where that simplistic approach might not be too wonderful .. some years ago I was doing some audit and contract setup work for a mining operation in a developing country.

The routine (closed contract) transport was a flight of around and hour and a half from the coast to the mine site. For reasons which are not important, the air service was suspended for some time and the trip was done by a combination of 4 wheel drive, speedboat, motor launch, clambering over rocks, dodging headhunters, and so forth.

This alternative trip took a day and a half. Having done the trip a few times, I shall have some wonderful tales of excitement and near death experiences to tell my grandkids ...

I don't know whether anyone was killed on the alternative trip ... certainly there were a few injuries from road accidents .. and project management personnel were terrified of the whole exercise .. they wanted their you-beaut airservice back on line ...

(b) impose the requirement of a big aircraft .. which might not be able to do the job physically ... which puts us back to the terrifying hazards of (a) ... or, if the costs are too high, might put the project out of business .. which really doesn't help anyone at all ....

(c) try and come up with a set of additional requirements which might go some acceptable way towards overcoming the known deficiencies of the typical small aircraft operation ?


Hopefully, this latter is the direction which this thread might take .... here is a problem we can see .... now let's debate reasonable and achievable ways and means to reduce its undesirable consequences .....

[I Fly]

If this argument is perused to the end's degree we will need a major rethink in town planning. Everyone lives within walking distance of a runway capable of handling B 747s. 777? No, not enough engines. I seem to recall this discussion started on the other thread because a government employee had to get out of a Boeing and into a Bonanza to finish a trip. How did they get to the airport in the first place? By train? By Taxi? was it a Holden or a Rolls Royce?
In February 1999, CASA under DS, put out a pamphlet informing passengers as to what safety level they could expect on what aircraft. It also stated a light twin engined aircraft (the picture was a Chieftain) was twice as safe as travelling the same distance by road. (It did not mention whether the road travel was by Rolls Royce or GoGomobil). From that pamphlet passengers could get an informed idea as to what safety level they could expect. They then have a choice.
We do not use a sledgehammer to crack a nut. We also don't use a 1oz hammer to smash a wall.
We need to develop aircraft of various sizes and various performances to fit into various strips AND MAKE EACH AS SAFE AS WE POSSIBLY CAN. No matter how much money I spend on my Maule, it will never be as safe as the B747. No matter how much money I spent on my B747, it will never fit into Yaranderry.

[411A]

Interesting thread this..

Lets look at things from a practical angle.
The smaller twin engine piston machines used in commuter/charter services are reasonably robust, IF maintained and flown properly. The Cessna 400 series (of which I am familar as I own one) have now definate life limits imposed on the wing structure....beyond a certain number of hours, a wing strap kit must now be fitted (285 man/hours, not cheap) as the design was never intended to be operated really high hours/cycles. But, if properly and thoroughly inspected, will do the job intended, quite safely. Operationally, these types must NEVER be overloaded as their engine inop flight profiles are meager at best. And there in comes the rub...to make money, seats must be filled, or fares must be raised, to cover the expense, and the temptation to fill up fuel, baggage and pax is strong indeed.

Small twin engine turbine types have more reliable engines, and some were designed for higher hours/cycles, but still require intensive maintenance. These types, due to their more reliable and powerful engines, generally have better performance and greater safety margins....but of course do not have the redundancy level of part 25 aeroplanes.

Seems to me that maintenance is the key element in the safer operation of these machines.

[Genghis the Engineer]

I would venture that it is A key element. To say that it is THE key element ignores a lot of very important other factors.

The difference of-course is that most of the other issues (manufacturing QA, handling qualities, performance, operating data, basic structural integrity, powerplant matching, crashworthiness, etc.) only need to be got right once per type or once per aeroplane, whilst maintenance needs to be got right over and over again.

I don't think we should also lose track of the far greater training standards, currency standards, and the fact of usually a 2-crew or greater compared to single pilot, which is associated with a part 25 aeroplane.

G

[411A]

Yes, would agree that two crew is a better idea, but then...
IF the small type is fitted with a "quailty" autopilot (S-tech comes to mind) then that second pilot is really not needed, provided that the PIC is properly trained in the machine AND knows how to use the autopilot properly.
So...could we say maintenance AND training?
A tough combination....sometimes.

[Disco Stu]

I know many owner/operators that know their own (single pilot)aircraft systems/performance intimately. I know equally as many RPT pilots that know the aircraft they fly for work in the same manner. The obvious difference is one is single pilot, the other, a multi crew airline environment.

Certainly the training is different but where the real difference is obvious, one is part of an ongoing CHECK and training system, the other is not.

We seem to have a pretty good handle on the mechanical (design, construction & maintenance) of an airframe, where we still seem to be always let down is in the human factors area. In spite of what some would have us believe, engineers and pilots are only human and therefore prone to all the foibles, emotions and simple human traits that are present in all of us.

I am not advocating the use of robots (I am not a bean counter) instead of humans, what I do support though is training, checking, more training and more checking. This long with a viable Safety Management System is a major part of the answer. Simply complying with the regulations should only be seen as a minimum standard (some do), overlay them with an active SMS and you go a long way to not only a safe operation but adding the benefit of quality as well.

Thanks to the Admin people at PPRuNe for adding this forum. Trying to discuss Safety CRM and QA in the other forums was a waste of time and energy.

Disco Stu

[OzExpat]

As we're clearly talking about this in relation to the "end user" of the product, I'd have to go along with 411A. Whole books could be - and indeed have been - written about "maintenance" and "training", as separate issues. In reality, they are two sides of the same coin, having their own standards and QA.

The best we can ever hope to do, IMHO, no matter what type or sort of aeroplane we're talking about, is to ensure that those two key ingredients are matched as well as is feasibly possible. I'd have to say that there's, currently, room for improvement in both areas - but we probably won't see that improvement until they are universally regarded as the two sides of the same coin.

I guess that the next problem is how to make that happen...

[john_tullamarine]

Everything we do in life involves choices in many things .. including risk perception.

Often the choices made are reasonable and justified (jumping off a cliff probably attracts a higher likelihood of death than does retiring to one's bed in the late evening so most of us prefer the latter activity) .... sometimes irrational (the general public perception is that some activities, in particular the nuclear and aviation industries, are inherently riskier and more dangerous than other, more routine, activities whereas the historicals show otherwise in many cases).

It would be nice if we (as typical Joe Publics) could be rational and assess risk on the basis of objective historical data .. ie incident and accident stats .. or rational analysis of likely outcomes ... but the reality is that the thing is a combination of fact and gut reaction.

Indeed, it is a case of "horses for courses".

In the same way that the trainer and training system makes a big difference to the horse's performance ... the requirements and constraints which we (as Industry people) or the customer (in contractual impositions) may choose to impose can, and do, have a significant impact on the risk levels.

While we all should laud the attitude to "be as safe as we possibly can", a more practical approach is to seek the highest reasonably achievable levels of safety (risk management and control). For example, if a small gain is going to cost a King's ransom, then there may be a rather difficult risk cost-benefit decision to be made. This is the philosophical sort of thing which the FAA (and other NAAs), for instance, tries to address in its NPRM process.

If the proven help-to-keep-us-out-of-trouble processes break down, the 747 can be dramatically less safe than a lightie ... if the heavy crew, for instance, chooses to bust minimum levels and ignore GPWS warnings in IMC or at night, or the operator pushes its crews to carry an inappropriate range and combination of MELs, while the lightie pilot and operator choose to be more sensible, then perhaps I might prefer to travel with the latter ?

There is a need to be rationally sensible. As an example of the contrary view, we have seen a number of recent times rotary accidents in various countries where maintenance (or lack of) or certification requirements (lifed items, etc) have been ignored, abused, or misused.

The question of multicrew ops is a vexed one in the absence of a well designed and implemented training program. Unfortunately we see contracts at times which impose on the small aircraft operation a well intentioned but ill-considered requirement for two crew members (often no more than a requirement to have a second pilot .. period .. I guess that at least provides a conversation companion for the leftseater ?). Without some sensible requirements for anciliary activities designed to produce an effective multicrew operation .. the end results may be very much less than desired or expected by the end customer.