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 takeoff, 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 takeoff 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 takeoff could
have been identified and prevented during pre-flight checks.
Aircraft physical inspection, engine run ups and on takeoff 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
takeoff; - the engine not 'sounding' or 'feeling' normal, such as general
rough running during the takeoff 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 glidespeed 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 takeoff is a complicated issue. The
ATSB's booklet Avoidable Accidents: Managing partial power
loss after takeoff in single-engine aircraft examines it
in depth, breaking it down into the same sequence of events as if
conducting a flight.