To: helmet fire
“You would have to catch a commercial airliner every day for 26,000 years to guarantee being involved in a fatal accident. Flying a commercial airliner is 9 times safer than driving a car”.
These types of statements are based on the party line put out by all of the airlines and are based on seat miles traveled. Here is an example. Airline A has thirty aircraft that are capable of carrying 200 people. Each of these aircraft flies full from LAX to JFK and return a distance of 6000 miles.. .Each aircraft makes one round trip a day. Each trip takes a total of 9 hours round trip. In one day they accumulate 72,000,000 million passenger seat miles. In one month they accumulate 2,160,000,000 passenger seat miles. In one year they accumulate 788,400,000,000 passenger seat miles. On the last day of the year they lose one aircraft and 200 passengers plus crew due to the failure of a single part. In their advertisement they state proudly that they have had only one major accident and having flown 788,400,000,000 passenger seat miles. However they have accumulated only 98,550 flight hours on the 30 aircraft. The FAA states that the loss of an aircraft or death to a single passenger caused by a single point failure can occur no more frequently than 1 10 9 flight hours for the fleet or one time in a billion hours.
As I indicated in my post above there are many single point failures that have downed aircraft and they occurred long before the respective fleets had accumulated 1,000,000,000 hours of operation.
Here is another way the FAA obfuscates the truth about the calculated safety of an airliner. Hopefully you have some knowledge of a Fault Tree Hazard Analysis. It consists of and gates and or gates that represent different elements of a given system. The place these various gates in a logical order so that it can be shown how the elements of the system are related to each other when the system / systems are operational. In every case the top gate in every system is a “and” gate which means that several things have to occur at the same time for the system to fail. Using Boolean Algebra it can be “Proven” that the system has a predicted rate of failure of 1 10 12th or up to 1 10 17th. The problem is that if any one of these systems fails you lose the aircraft so, to truly represent the operational safety of the aircraft as a total entity each system must migrate upward to an “or” gate. Using the same Boolean Algebra it can be shown that the aircraft as a total entity has a failure probability of less than 1 10 9th. The FAA regs. do not require the last step as to do so would indicate that the aircraft is not as safe as they state in the regs.