With the tragic and unexplained loss of Malaysia Airlines Flight MH-370, a review of general airline accidents and safety is the theme of this post.

This post is review of the statistics of occurrences which can be an invaluable source of information that allows for analysis of incidents.  The statistics presented in this post refer worldwide commercial jet planes with a maximum gross weight of over  60,000 pounds. Aircraft manufactured in the former Soviet Union are not included.

1. Growth in air traffic
Air traffic increased exponentially between the beginnings of aviation and 2001. After the attack on the World Trade Center, however, many airlines came into financial difficulties and air traffic started to drop. Two years down the line, traffic picked up again.

Air Traffic Growth

In 2008, airplanes travelled a record 46.3 million flight hours. This is an important to number into remember when interpreting statistics and failure rates. An event may have only a 1 in a million chance of happening, but it will, statistically, occur several times a year.

The following graph shows the total number of certified commercial jet airplanes with a maximum gross weight of over 60,000 pounds. It does not include aircraft manufactured in the former Soviet Union.

Number of aircraft in operation

The number or aircraft in operation keeps increasing in a need to meet growing trademand for air travel. Despite congested airspaces, collision risk remains very low due to new technologies that allow for accurate position and altitude measurements, to assist both crews and Air Traffic Controllers to prevent collisions. For example, in order to accommodate all traffic over some oceans, specific airspaces where aircraft are separated vertically by only 1000 ft were created.

Average Flight Time

The graph above shows that the average flight time has also increased with from 1970 to 2008. Modern aircraft can perform 22-hour non-stop flights and fly halfway round the world without landing. These very long-haul aircraft are becoming ever more common and statistically have lower incident rates.

2. Drop in aircraft accident rates
Although the number of accidents per flight has been decreasing with time, the number of fatalities per year has been variable, without a corresponding reduction. in number.

Accidents and Fatalities

Aircraft accidents are less likely to occur today than in previous years. Nevertheless, the growing number of aircraft in operation and their increasing capacity means a reduction of onboard fatalities cannot occur.

(*)External fatalities include on-ground fatalities as well as fatalities on other aircraft involved.

3. Scheduled passenger flights are less likely to be involved in accidents than other types of flights
Statistically, you are less likely to be involved in an accident when flying a regular scheduled flight than when taking other types of flights (unscheduled passenger flights, charter flights, cargo flights, and all other types of flights). That conclusion is reflected in the following graph:

Scheduled passenger operations and other kind of operations

The above graph also shows that scheduled passenger operations are 5 to 6 times more common than other types of operations.

4. When do accidents occur?
Between the time a passenger boards an airplane and the time they disembark, there are 6 distinct phases:

• Taxi: the aircraft taxis to reach the runway, or it taxis to the gate after landing.
• Take off and initial climb: the aircraft accelerates, lifts off and starts climbing.
• Climb-out: the pilot retracts the slats/flaps, and the aircraft climbs until it reaches cruise altitude.
• Cruise: the aircraft flies at a more or less constant altitude. This is generally the longest phase of the flight.
• Descent and initial approach: the aircraft descends for approach to its destination airport. Air traffic control may request the aircraft to hold while earlier arrivals are cleared for landing.
• Final approach and landing: the aircraft, in landing configuration and aligned with the runway axis, approaches the runway threshold, then lands and slows down.

When do accidents occur?

Over half of all accidents occur during the final approach and landing stages. These aren’t the most devastating accidents, however. A runway overrun may result in only a few injuries, for example.

Fatal accidents are more likely to occur during the climbing stage. If the aircraft leaves the gate with undetected mechanical faults, these may affect the aircraft during the climb, and could prove dangerous. All aircraft systems are under the greatest load during take-off and climb-out. If the crew believe a failure requires the aircraft to land as soon as possible, they will decide to perform an IFTB (In-Flight Turn Back).  This maneuver could prove difficult to execute however, as the aircraft may have already be operationally compromised with failed or reduced control sytems.

Most accidents and fatalities take place during the departure (take off / climb) and arrival (approach/ landing) stages. During these phases aircraft are closer to the ground and in a more vulnerable configuration than during other flight phases: the crew have to deal with a high workload and reduced margins for error.

5. Root causes of accidents
It is quite rare for an accident to be explained by one single cause. Almost every incident is the consequence of a chain of events and accident reports usually identify the main cause and a number of other contributing factors. The following graph shows the distribution of main causes identified in plane crashes.

Root Causes of Accidents

The main root cause is human error. This does not necessarily mean pilot error. In order to try and eliminate this as a source of accidents, crews are remandated to follow a strict training routine. Aircraft failures are mext most common cause, but these are less likely in modern aircraft.

6. Aeronautical terrorism
Airport security measures and increased vigilance can protect from aeronautical terrorism (bombing and hijacking). It is without a doubt the safest place in an air journey is in the sterile area in the airport prior to boarding.  Comversely, aircraft are very vulnerable to attacks, because they are defenceless, and because a plane crash is newsworthy highlighting a terrorists cause. Cargo bay containers can be bomb-proof, but not the aircraft itself, as the added weight would make them too heavy to fly.

Increased security awareness have seen many measures implemented in a bid to prevent such attacks, with the result that the number of terrorism acts has dropped with time. When it comes to terrorism incidents and fatalities, there can be no trends due to the randomness of these actions. New and larger aircraft carrying a lot of people may become targets of choice for terrorists, which can lead to extremely deadly attacks.

Terrorism in Aviation

7. Conclusion
Air travel safety is a data-driven activity. The number of aircraft in operation is constantly on the rise but accident rates continue to fall, making air transport the safest of all means of transportation.

The increase in flight length also contributes to the drop in the number of plane crashes. As accidents are more likely to occur during the take-off and landing phases, a long-haul aircraft which perform only one or two long cycles a day are less likely to be involved in an accident than a short-range aircraft which may perform ten short cycles a day.

The introduction of regulations and checks by authorities and the growing experience of aircraft manufacturers, and increased technology and safety systems all contribute to the improvement in the safety of air transport.

As the number of aircraft now operating continues to grow, even though the rate of accidents per flight may drop, the actual number of accidents will increase. Since aircraft carry an ever increasing number of people, the number of onboard fatalities will also rise.

Disclaimer:
This post doees not include data from aircraft from the former Soviet Union or airlines from countries from former Soviet republics. These aircraft and airlines are statistically more likey to be involved in an aircraft incident.

As of 10/07/2013, airlines from Kazakhstan, Kyrgyz Republic and 287 other carriers world-wide are banned from flight within the European Union for failure to meet accepted safety standards.