The Iranian Air Force Boeing 747-200B suffered significant damage during an engine test run at Mehrabad International Airport in Tehran. The aircraft was undergoing precise D checks for over a half of a decade before this test run.

As of now, it is unknown what exactly led to the test failure. According to the Independent Persian, the test caused the Queen of the Skies to either suffer a jump of chocks or a brake failure. The incident followed the jumbo’s D check stint.

As Lufthansa Technik points out in documents regulating aircraft maintenance rules, this testing procedure is also known as a heavy maintenance visit (HMV) and it is the most comprehensive and rigorous check for a jet. The inspection is required approximately every six to ten years. Depending on the number of technicians involved, it can entail 30,000 to 50,000 man-hours of labor over a period of four to six weeks to complete.

As it is the general overhaul of an aircraft, during the D check, the entire structure is inspected down to the smallest detail. This implies that in some cases, the whole aircraft could be taken apart for investigations, even the paint may need to be completely removed for a complete inspection of the fuselage metal skin.

The requirements and effort involved in this type aircraft maintenance check make it by far the most expensive aircraft inspections and, as it is counted by Aircraft Value News, the Boeing 747-200B D check costs could reach more than  €2.2 million (USD$2.5 million). 

The Iran government’s 747-200B could be called an industry veteran, as the average age of the fleet in the Force reaches 47.6 years, based on planespotters.com. With the aircraft being over four decades old, it is not surprising that it had to undergo such a thorough inspection. According to the website, the jet used to be registered as YI-AGN, but it currently holds a registration number 5-8106. Currently, the jumbo is the only Iranian Air Force’s unit of the type. It joined the flag carrier of Iran’s military in May 1997 after the country took it on from Iraqi Airways as war reparations.