The U.S. Federal Aviation Administration (FAA) has ordered the mandatory inspection of nearly 200 Boeing 737 aircraft around the world after fatigue cracks have been discovered on several aircraft.

Southwest Airlines flight 812 was on a routine journey between Phoenix, Arizona and Sacramento, California on 1 April. But the ordinary became extraordinary when a 5 to 6 foot (1.5-1.8 meter) long hole blew open over the passengers, causing a rapid decompression of the cabin. What ensued was an emergency descent to a safe breathing altitude followed by an emergency landing at an Arizona military air station. There were no serious injuries reported (one flight attendant was slightly hurt) but the scare that passengers had in the air has airlines and aviation bodies looking a little closer at the planes we fly in.

The aircraft in question is a Boeing 737-300, delivered in 1996 to Southwest Airlines. This aircraft has over 39,000 take-offs and landings, collectively known as cycles. Southwest is an airline known for its high utilization of aircraft, many flying as often as 9 journeys in one day. The frequent compression and decompression of the fuselage adds to the possible formation of microscopic cracks in the metal over time, particularly where two or more pieces are joined together. Aviation bodies throughout the world stress the need for regular checks of airframes, particularly after a specific number of cycles is reached. Often, the recommendations start from the manufacturers themselves through service bulletins – essentially maintenance how-to steps for performing particular inspections or repairs. From there, aviation bodies put forth directives or other mandates to ensure that these recommendations are being followed. There is a flaw to this practice, however, and it stems from the natural tendency of agencies to be more reactive than proactive.

The FAA has issued several Airworthiness Directives mandating inspections of aircraft for metal fatigue over the years, and not just for the 737s in question. The problem is that most of these directives have resulted from specific incidents and only cover the sections of the planes in question. So, if a crack appears near a door seal of one aircraft, then the directive orders airlines to check, inspect, and repair any anomalies in that section only. Later, another directive could be issued if something occurs on another part of the plane.

Airlines already perform varying degrees of maintenance ranging from visual inspections by flight crews and maintenance personnel, to complete maintenance overhauls during which aircraft are given an inside-out makeover. The outer skin of the aircraft is typically scanned for microscopic fractures during these overhauls using electronic methods of detection and repairs are made if any cracks are found. With all this scrutiny and technology, how could a breach of the fuselage still happen? It goes back to the reactionary way of doing things. The section that ruptured on the Southwest Airlines plane was not an area previously thought to be vulnerable. Therefore, it was not required to be so thoroughly inspected. That will likely change.

The FAA has now mandated that new inspections be conducted on 737-300, 737-400 and 737-500 aircraft that have reached a specific threshold of takeoffs and landings (30,000 cycles). Though the quick reactions of Southwest Airlines to voluntarily ground and inspect its 737-300s, and of the FAA for subsequently – and rather quickly – issuing an order for more thorough inspections are encouraging, questions remain as to the effectiveness of current practices. There is no reason to believe at this time that poor maintenance is to blame for the incident, but with aircraft being so highly utilized today, wouldn't it be prudent to bring safety practices in line with the way airlines use their aircraft?

A much more comprehensive inspection of airframes could be very costly to the airlines, especially with their money-making machines out of service. But it may be time for a complete "body" check of aircraft instead of the patchwork of service bulletins, recommendations and directives we have today. They have served us well over the years and have helped make aviation safer. Yet there are those rare instances when something does go wrong and we must realize that every stroke of luck in this industry should be paid back with a higher degree of precaution and safety no matter what the cost.

The National Transportation Safety Board (NTSB) in the U.S. is investigating the incident with Southwest flight 812 and expects to issue a final report within 12 months. This timeframe is typical of accident and incident investigations.