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Single Turbine Engine Aircraft
Is Two safer than One? No!

The State of Play

(SETA Report RA/2005/03. Issue 8. 6 July 2007)

Single-Engine Commercial Operations

1. Introduction

Until 1988, virtually all single-engine aeroplanes operating commercially were restricted to operations by day, in VMC and such that a suitable forced landing site was within gliding distance. The International Civil Aviation Organisation (ICAO) in its Annex 6 (Operation of Aircraft, Part 1 – International Commercial Air Transport – Aeroplanes) had incorporated these restrictions in its Standards since 1948. These are intended to be the minimum standards of safety for all of its member States for international operations and reflected the relatively poor engine reliability typical of the 1940s. States are expected to reflect the ICAO Standards and Recommended Practices (SARPs) in their national regulations.

In 1988, the USA changed their regulations to allow commercial operations by single-engine aeroplanes at night and/or in IMC (SE-IMC) for cargo flights only. Canada then allowed both passenger and cargo operations in 1993. Australia, New Zealand and South Africa followed from 1997. The USA then extended its approvals to include passenger operations in 1998. The USA, Canada and Australia in particular published a safety-benefit analysis and all report satisfactory experience in service. Now countries responsible for more than half of the world’s civil aviation approve SE-IMC and the three main single-engine turboprops (Cessna C208, Pilatus PC-12 and Socata TBM 700) have together flown more than 10 million hours, about half on commercial flights. Over 2000 modern single engine turboprops have now been delivered to 70 countries.

Europe’s Joint Aviation Authorities produced an Advanced Notice of Proposed Amendment (ANPA) in 1998 and has since developed three Notices of Proposed Amendments (NPAs), each subject to extensive work, analysis and consultation. The approach has been more conservative than previous countries’ requirements with a limited ‘risk period’ allowed in the cruise (when the aircraft is out of gliding range of a Landing Site), as well as a requirement for a range of systems and equipment enhancements, more comprehensive experience and training for the crew, and an engine reliability requirement of a ‘Loss of Power’ event (such that a forced landing is inevitable) of less than 1 per 100,000 hours (at this time limiting the approval to turboprops).

Meanwhile, ICAO tasked its Operations Panel with a range of amendments to Annex 6, including SE-IMC for single turbine-powered aeroplanes. The Ops Panel formed a Working Group, with two subsidiary groups, to review all aspects of the issue and to draft the amendments. The result of this work was approved and supported, with very minor amendments, by the Air Navigation Commission. After circulation to all 187 member States of