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What: Austrian Airlines Boeing 767-300 en route from Vienna Austria to Washington DC
Where: Vienna
When: May 27th 2011
Why: After takeoff, the gear would not retract.

The pilot returned to make a safe landing in Vienna; repairs were made and the flight left again less than an hour later.

Anonymous Expert Opinion
One common occurrence in Commercial Aviation is when a maintenance person forgets to remove the Landing Gear Safety Pin that is connected before starting the push back procedure during the aircraft start-up. It happens that that pin prevents the hydraulic system to actuate the nose gear allowing the tractor to freely steer the aircraft free from the gate. However that pin also locks the landing gear in the “down” position preventing the hydraulic system to retract in when commanded by the pilots. The result is that the aircraft is prevented from retracting its landing gear (one pin prevents them all) and returning is mandatory.

If the airplane is engaged in an intercontinental flight (thus carrying a huge amount of fuel) the crew invariably must dump a great amount of fuel in order to reduce the weight to within the manufacturer’s certified maximum landing weight in order to perform a safe landing. After dumping the fuel as the aircraft’s weight reaches its maximum allowed for landing the crew land the airplane. Unfortunately it causes delays and it is a nuisance, although not a harmful one. The worst part is for the maintenance crew whom was responsible for the tow out procedure to explain to his (or hers) superiors the quite expensive forgetfulness.