An emergency landing by a British Midland 737 G-OBMM in 1995.
Shortly after takeoff the captain noticed that the oil level was dropping and
immeditely diverted to Luton.
The problem was found to be caused by engine covers not being replaced after a borescope examination the previous night.
Report :
http://www.aaib.dft.gov.uk/cms_resou...pdf_502864.pdf