German officials on Wednesday launched an investigation into what caused a military Airbus A400M plane to break down on the tarmac during a visit by Germany's defense minister to Lithuania.

Engineers reportedly discovered an oil leak in one of the plane's four engines during a routine maintenance check, as Defense Minister Ursula von der Leyen was visiting German NATO troops stationed in Lithuania.

The visit marked von der Leyen's first foreign trip on the aircraft, which Germany's military had only received in December. The plane was intended to showcase the capabilities of Europe's largest defense project. Instead, it delayed von der Leyen by half-an-hour and forced her to fly back on a 50-year-old "Transall" replacement aircraft.

A series of technical glitches

The breakdown is just the latest incident following years of delays and technical incidents for the A400M.

It remains unclear whether the latest issue revealed a new technical challenge. A spokesman for Germany's air force said engineers were investigating the engine's hydraulic system but declined to provide further details.

Airbus has already written off some 5 billion euros ($5.34 billion) in its program with Germany's Defense Ministry after previous aircraft experienced gearbox problems and suffered fuselage cracks.

An Airbus spokesman said, "We are shocked and deeply regret that the defense minister and her delegation suffered significant travel consequences as a result of the breakdown of an A400M."

It means that just one of Germany's eight A400M planes is currently in service, with three currently in repair, three going through routine inspections and one being refurbished.

Europe's largest defense project years behind schedule

Germany's A400M program is years behind schedule, with the federal government's share of the costs having risen from an initial estimate of 8.1 billion euros to 9.6 billion euros.

Germany is the largest customer of A400M planes, having initially agreed to purchase 53 of them from Airbus. The Defense Ministry maintains that it has a good contract with Airbus that allows it to demand compensation for delays and other technical issues.

The A400M was due to completely replace the older "Transall" aircraft by next year. Officials now expect that transition to be completed by 2022 at the latest.

The new aircraft was developed as part of a program for seven European NATO states with an initial estimated cost of 20 billion euros.

Tuesday's episode coincided with reports that Germany is looking to maintain access to more A400M planes through a pooling agreement with several countries, backtracking on initial plans to sell 13 on of the 52 it has agreed to buy.

dm/sms (dpa, AFP, Reuters)