Before revision: "Technical" page on harrier.org.uk website, viewed 2013-11-24 Contamination On about 1 in 5,000 flights, bleed air used for air conditioning and pressurization can be contaminated by chemicals such as oil or hydraulic fluid.
After revision: Contamination On about 1 in 5,000 flights, bleed air used for air conditioning and pressurization can be contaminated by chemicals such as oil or hydraulic fluid.