A.P. 129 RAF Flying Training Manual, Part I - Landplanes

[NZtyphoon]

Thanks 41Sqn; attached is another explanation of boost types used by RAF engines from R A Beaumont A.F.R.Ae.S "Aeronautical Engineering: A Practical Guide for Everyone Connected With the Aero Industry"

(3) Override Boost - For the greatest possible power output for take-off or emergency, an increase in pressure above the normal take-off boost is permitted on some engines. This condition is used in conjunction with a special fuel. (p. 106)

The wording is similar to A.P.129, apart from noting that override boost was used in conjunction with a special fuel.