An engine failure was one of the most typical exceptional circumstances in the era of piston engines–to such an extent that the uneven operation of an engine was not exceptional. Cylinder changes could be carried out by the local mechanic in the open air, and adjusting the ignition of an unevenly running engine was almost a daily routine. As a result, the possibility of total engine failure was already taken into account in the performance calculations for takeoff, and pilots were trained in how to operate in case of engine failure.
The probability of engine failure decreased significantly with the introduction of jet engines. This was because the pistons moving back and forth under major loads were replaced with disks moving more evenly–the rotors of the compressor and the turbine. At the same time, the number of valves and other moving parts was significantly reduced. Thrust increased hugely, and margins to terrain in case of engine failure were markedly bigger. Regardless of all this, we still prepare for engine failures with the conservative approach we’ve learned. Takeoff is the most critical stage in terms of engine failure, but it has to be considered in other stages of the flight as well. Performance calculations are made by the pilots before each takeoff based on the prevailing conditions and the takeoff weight. We make preparations that, in case of engine failure, we can either stop the plane on the remaining runway, or continue the takeoff with one engine out and clear the obstacles ahead with the safety margins specified by the authorities. Cockpit procedures in case of engine failure are revised every day before the first takeoff of the day. The flight path in continued takeoff (which may, depending on the obstacles, be something other than just straight ahead) is discussed before each takeoff. The skills of the pilot are checked in the simulator at least twice a year. I can confirm that these matters are rooted deep in the minds of pilots, although with the current engines, the likelihood of an engine failure during a pilot’s entire career is less than one event. The probability of a failure in which the engine shuts down in a controlled manner before major failures occur (In Flight Shut Down – IFSD) is around one / one million flight hours, and the likelihood of a total engine failure is at least ten or perhaps even one hundred times less likely than that. Giving an exact number is difficult as reliability continues to improve with increasing numbers of non-failure flight hours.
This year, Finnair has had a couple of events in which an engine has been shut down during flight. In twin engine planes, this means landing at the nearest suitable airport for safety reasons. We don’t continue to fly with just one engine. In many cases, passengers don’t even notice that an engine has been shut down until the commander has made an announcement. The Safety investigation authority doesn’t investigate such events either–that’s how harmless they are. In all recent events, the pilots have noticed the situation even before receiving alerts from the plane’s warning systems. Such events do, however, trigger the company’s internal Safety Management System (SMS), which is based on the EU regulation. We determine, for example, if there are any common denominators in such cases; whether maintenance, for example, has been carried out according to the requirements, whether the spare parts and materials used meet the requirements, etc. All of this is done in close cooperation with the engine manufacturers, as it is also in their interests that the engines operate without problems.