The CAA General Aviation Report - Occurrences, published on 6 June gives the following insight to the problems:
"RPM decay during display practice.
A progressive level of RPM decay was experienced during the course of the sequence and was unacceptable towards the end of the flight. During the penultimate stall turn, an RPM decay to 1700 was experienced with associated oil pressure drop to 30psi. Tech Log entry made. Engineers report states that following installation of the MT propeller on this a/c type, several confirmed reports of RPM decay have been reported during certain aerobatic manoeuvres especially in vertical or near zero G conditions. The inverted oil system is suspected as being a contributory factor and the manufacturers and maintenance organisations are in consultation. All company owned a/c have been temporarily removed from operation until advice from the OEM has been provided."