Partial engine power loss is when the engine provides less power than commanded by the pilot, but more power than idle thrust.
This kind of power loss is more complex than a complete failure, and it can be much harder to stay ahead of the aircraft. The pilot is thrust into a situation where the engine is still providing some power; however, the power may be unreliable, and the reliability may be difficult to assess. As a result, pilots are uncertain about the capabilities of their aircraft, and what their options are-a situation that has led to loss of aircraft control at heights close to the ground, and fatal outcomes.
And because it's not a substantial part of flight training, pilots tend not to think about it beforehand. Compared to the scenario of total power loss after take-off, they don't think about how they would react in such a scenario. As a result, when it does happen, it can turn into disaster very easily.
How to manage partial power loss after take-off in a single-engine aircraft
1. Plan
Acknowledging the possibility and establishing different strategies to deal with a partial power loss before flight will give you an advantage. By planning your response ahead of time, you reduce your mental workload, mitigate some effects of decision making under stress, and give yourself the confidence to carry out positive actions in the emergency situation.
2. Check your aircraft before you take off
Many partial power loss incidents occurring after take-off could have been identified and prevented during pre-flight checks. Aircraft physical inspection, engine run ups and on take-off engine checks can significantly help prevent partial power loss occurring. Many instances of partial power loss have been found to be fuel and spark plug related, which can exhibit physical symptoms such as:
- an rpm drop higher than the maximum prescribed by the manufacturer during run-up checks;
- a lower than minimum static rpm on application of full power on take-off;
- the engine not 'sounding' or 'feeling' normal, such as general rough running during the take-off run.
3. Maintain control of your aircraft
If you still experience a partial power loss you need to respond immediately. Taking no action is not an option. The first priority is to maintain control. Pilot actions have included turning back to the aerodrome or conducting an immediate forced landing on or off the aerodrome; however, the height of failure, wind speed and direction, traffic and terrain are all factors which will influence this pre-planned option. Maintaining glide speed and no more than a moderate bank angle will ensure you maintain control. Arriving at the ground with wings level and with the aircraft level with terrain, rather than after a stall and or spin can make all the difference.
More information
Partial power loss after take-off is a complicated issue. The ATSB's booklet Avoidable Accidents: Managing partial power loss after take-off in single-engine aircraft examines it in depth, breaking it down into the same sequence of events as if conducting a flight.