* How safe are aircraft?

A scientific, very respectful and well-thought reply to the popular question "Do you believe in UFOs?"  This book evolved as a reply to one of the most frequent questions that I used to hear from the public when I was working in an astronomical observatory: "Do you believe in UFOs?". That seems an odd question to ask to scientists, but after researching conscientiously for about a full year, I discovered, to my surprise, that mainstream Science has a few things to say about the topic.  This book is not about conspiracy theory, "NASA is hiding the truth", or much less, that flying saucers have already landed on the lawn of the White House. Rather, it is a book about what is the most rational reply that a scientist, or in my case, a science writer, can offer when people insist on asking that question.  As one advances through the chapters, explores the following rationale: Is there life in the Universe? The answer is yes: us. Are there civilizations capable of spaceflight? The answer is again yes: us. Can we expand those two questions? Can we answer also: "them" and "them"?  All illustrations are also available at naturapop.com










Photograph: While on the one hand solo amateur piloting, navigation by eye and reciprocating engines can lower air safety to levels comparable to motorcycles', the reality is that professional team piloting, navigation by instruments and sophisticated turbine engines make airlines have a higher safety rate per kilometer than any other means of transportation. In the photo, a Boeing 737-800 (ZK-PBF, "Tepu'itea") of Polynesian Blue in Wellington International Airport, Wellington, New Zealand, on 2 March 2008. Photo credit: Follash, via Wikimedia Commons.

NUMBERS AND MORE NUMBERS, BY TYPE OF AIRCRAFT AND TYPE OF OPERATION: HOW SAFE ARE AIRCRAFT?
We know that 1 in 80 people will die in a car accident some day, while 1 in every 6500 people will die in a aircraft crash. Of course, fewer people travel by air than by car. Recognizing this, what can be done is to compare the same trip in different means of transportation, either in terms of kilometers traveled, elapsed time, or simply by the fact of embarking. 

The Cessna 172, the world's best selling aircraft, has an accident rate of 62 per million flight hours, although only a portion are fatal accidents. In 85 percent of the cases the cause is pilot error. Its brother the popular Skylane has a rate of 92 accidents, both minor and serious, per million hours.

The modern Cirrus SR has a built-in parachute, but still 14 of its accidents per million hours are fatal.

The Beechcraft Bonanza, which has been in production for more than six decades, has an accident rate of 47 per million hours, but more than half are minor accidents with no serious injuries or fatalities.

Notably, its brother the twin-engine Beechcraft Baron has the same rate. While twin-engine airplanes have a backup engine in case of failure of the other, it is usually very difficult to control a plane (at least a propeller plane) that pulls more towards one side than to the other.

The fastest piston-engine aircraft in production, the Mooney Series 20 has a general accident rate that falls to 19 per million hours if it is flown by instruments. This shows that it is better to be guided by instruments rather than by the human eye.

The aircraft with the highest rates are those of amateur construction, with 216 accidents per million hours, 55 of which with fatal outcome.

In propeller aircraft with turbine engines the accident rate is 20 per million hours if they have a single engine and 21 per million for two-engine airplanes. The fatal accident rate is 7 per million hours in both cases. The Beechcraft King Air C90 twin-turboprop, in production for more than four decades, has a rate of 19 accidents per million hours, 6 of them fatal. The lowest rate in this category is for the Beechcraft King Air 350 twin-turboprop, with a rate of 2 fatal accidents per million hours, followed by the single-engine Pilatus PC-12, with 3 fatal accidents per million hours.

The biggest difference appears to be not so much in the number of engines that the aircraft has but rather in the number of pilots. For example, if a twin turboprop is operated by a single pilot the probability of an accident is 1,5 times higher than if it is operated by two pilots.

For helicopters, the overall accident rate is 75 accidents per million hours. For piston-engine helicopters it is 199 accidents (22 fatal) per million hours, but drops to 61 accidents (11 fatal) per million hours if the engine is a turbine and 41 accidents (11 fatal) per million if the machine has two turbines. It is estimated that, in helicopters, 1 hour of flight equals 3 trips.

BUSINESS AVIATION

For business aircraft, the overall rate is 9 accidents per million hours, 3 being fatal. These averages are calculated from 14 accidents per million (3 fatal) for turboprops and 5 accidents (2 fatal) for jets.

Another way of analyzing these statistics is by number of flights. Thus, the overall rate of this division is 13 accidents per million flights, with 4 being fatal.

For small turboprops the numbers are 23 accidents (8 being fatal), for midsize turboprops 20 accidents (7 fatal) and large turboprops 15 accidents (6 fatal).

For small jets the numbers are 8 accidents (3 fatal), midsize jets 7 accidents (2 fatal) and large jets 5 accidents per million flights, with less than 1 of them fatal. The average duration of a flights in a business jet airplane is one and a half hour.

If a turbine-engine airplane (with or without propellers) is used for personal trips the accident rate is 10 per million flights, with 4 being fatal. If the plane belongs to a company the accident rate is 3 per million flights, with 1 being fatal. But if an airplane is providing air taxi service the accident rate rises to 44 accidents per million flights, 13 of them involving fatalities.

Again, if a jet is operated by a single pilot (in the few cases where it is allowed, depending on the size of the airplane and the type of operation), the probability of an accident is 2,7 times higher than if it is operated with two pilots. In fact, the rate of accidents resulting in fatalities increases 3,7 times.

Excluding charter flights and aircraft over 12 500 pounds (about 5,7 ton), the total accident rate for fixed-wing general aviation, both piston and turbine powered, in business or recreational flights, is 63 per million hours. The fatal accident rate is 13 per million hours.

AIRLINES

The global rate of fatal accidents involving turboprop airliners is 0,8 per million hours. On average, trips in this type of aircraft last 1 hour. The fatal accident rate for jet airliners is 0,2 per million hours. The average duration of each flight in this aircraft type is two hours. Combining both types of aircraft, the overall safety of airlines is 0,3 accidents with fatalities per million hours.

This can be analyzed again by airplane model. For example, the Beechcraft 1900 twin-turboprop, for 19 passengers, suffers 1 fatal accident per million flights. The turboprops ATR 42 / 72, for 40 to 70 passengers, have a fatal accident rate of 0,5 per million flights, while rival the de Havilland Q400 for 70 passengers has a rate of 0,7 per million flights .

As for jet models, the Boeing 707 / 720 has a fatal accident rate of 4 per million flights, the Airbus 318 / 319 / 320 / 321 family has a rate of 0,2, the Boeing 737-600 / 700 / 800 / 900 a rate of 0,1. The statistics are lowest for the Boeing 777 (first flight 1994) with 1 fatal air crash, the Airbus A340, with 2 air accidents but without fatalities in 20 years of operations, and the Boeing 717 (formerly McDonnell-Douglas MD-95) and the Bombardier CRJ-700 / 900, both without catastrophic air crashes to date even though each has flown more than a million times.

We do not consider the Airbus A380, the largest aircraft in the world, with capacity for 800 passengers, as it has not yet completed a million flights. For the same reason we disregard the Concorde, which up to its first and at the same time last accident had less than 100 000 flights, and therefore a statistical calculation would had said that it dropped from being the safest airline plane in the world to be the most dangerous, for that single accident.

However, not all passengers are killed in these accidents: if you are at 3 rows of seats from an emergency exit you are likely to survive.

COMPARISON WITH OTHER MEANS OF TRANSPORTATION

If what interest us are the kilometers covered, i.e., how safe is to get from point A to point B?, we see that 1 passenger dies in aircraft every 20 000 000 000 kilometers, 1 passenger dies in buses every 2 500 000 000 kilometers, by train 1 dies every 1 400 000 000 km, in vans 1 in 830 000 000, by water 1 dies every 380 000 000 km, by car 1 person dies every 320 000 000 km of travel, cycling 1 dies every 22 000 000 km, going on foot 1 person is killed every 18 000 000 km, and riding a motorcycle 1 every 9 000 000 km.

On the other hand, if what we want is the risk we take each hour we are traveling, that is, how safe is taking a tour?, statistics say that 1 death occurs every 90 000 000 hours spent aboard buses, 1 death every 33 000 000 of hours spent on trains, 1 person dies every 32 000 000 of hours spent on aircraft, 1 person dies every 20 000 000 of hours enjoyed aboard nautical ships, 1 every 17 000 000 hours aboard vans, 1 in 8 000 000 hours of car rides, 1 person dies every 4 500 000 hours of walking, 1 person dies biking every 1 800 000 hours of pedaling, and 1 person dies riding a motorcycle every 200 000 hours of exposure to that risk.

Finally, the most frequent question is usually: how safe is getting on this transport? In that case, per million trips, 1 person tragically dies en route every 230 000 000 times of travel by bus and every 50 000 000 travels by train, the same as by van. Going by car fatality says that destination is never reached once every 25 000 000 trips, the same as walking on foot. There is a chance of dying every 11 000 000 water travels, or doing 8 500 000 air travels, 6 000 000 bicycle trips, or 600 000 trips by motorcycle.

But in life it is virtually impossible to completely avoid risks. For example, 1 in 5500 people will die from tripping or slipping while standing and, surprisingly, 1 in 4200 people will die as a consequence of a fall from a bed or chair.

So fasten your seatbelt very tightly and have a nice trip!

A. L.

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Originally published in ABC Color on 16 August 2009. Photograph: While, on the one hand, solo amateur piloting, navigation by eye and reciprocating engines can lower air safety to levels comparable to that of motorcycles, the reality is that professional team piloting, navigation by instruments and sophisticated turbine engines make airlines have a higher safety rate per kilometer than any other means of transportation. In the photo, a Boeing 737-800 (ZK-PBF, "Tepu'itea") of Polynesian Blue in Wellington International Airport, Wellington, New Zealand, on 2 March 2008. Photo credit: Follash, via Wikimedia Commons.

A scientific, very respectful and well-thought reply to the popular question "Do you believe in UFOs?"  This book evolved as a reply to one of the most frequent questions that I used to hear from the public when I was working in an astronomical observatory: "Do you believe in UFOs?". That seems an odd question to ask to scientists, but after researching conscientiously for about a full year, I discovered, to my surprise, that mainstream Science has a few things to say about the topic.  This book is not about conspiracy theory, "NASA is hiding the truth", or much less, that flying saucers have already landed on the lawn of the White House. Rather, it is a book about what is the most rational reply that a scientist, or in my case, a science writer, can offer when people insist on asking that question.  Of course, "Do you believe in UFOs?" is, understandable, one of the most popular questions that common people ask (even if silently, to themselves) when they raise their eyes and look at the stars. So it has to be treated respectfully, and why not, given a well-thought reply.

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