Copyright of RotorSport UK Ltd
Document number RSUK0060
Page 75 of 101 Page issue 5.1, dated 10.06.14
Warning!
Overloading the electrical system will drain the battery (rated at 7Ahr). On a 914UL aircraft,
both fuel pumps are electrical, so draining the electrical system may stop the engine!
Two warning lamps are fitted to warn the operator of electrical problems:
1) The ‘GEN’ lamp is LIT when the alternator is NOT providing significant electrical energy to
the aircraft. This means that when the lamp is lit there is considered to be no on board
electrical supply other than the remaining charge in the battery.
When lit in flight, turn off accessories non-essential for flight to minimise battery drain. The
nominal aircraft load is 10A, and the battery is a 7Ahr unit. From the battery data, the battery
has a predicted capacity at 10A of 30mins, so ensure the current draw is minimised, and
expedite a safe landing well within those 30mins. Note that a 914UL engine requires
electrical energy to run the fuel pump and TCU, without which it will stop.
Note that in low light conditions the lamp may be seen to flicker gently, both at idle and in
flight. This is normal and no remedial action is required.
2) The ‘Low Volt’ warning light is LIT when the battery voltage drops to below 11.8volts. At
this voltage the low voltage load shedding relay will turn off landing, navigation, strobe
lamps, and the 12v panel socket (and heater fan, where fitted) – and light this ‘low volt’ LED.
This low voltage warning indicates that the alternator is unable to supply the aircraft electrical
demand, such that the battery is being drained. This could be due to alternator or other
equipment failure, or excessive electrical energy demand versus available alternator energy
(noting that the electrical supply from the alternator is dependent on engine rpm, as shown in
the supply graphs in the Rotax engine handbooks). If by pilot intervention the electrical load
is sufficiently reduced, or engine rpm increased to increase alternator output, then after a
short delay the lamp will go out and the automatically switched loads will be restored.
If the lamp fails to extinguish, and if the aircraft is powered by a Rotax 914UL, expedite an
immediate, precautionary, landing as the aircraft may have only minutes of battery power
remaining to power the electric fuel pump and engine TCU.
If the aircraft is powered by a Rotax 912ULS, and the lamp fails to extinguish, then the
requirement for an immediate, precautionary landing does not apply. This is because the
lack of electrical energy will not stop the engine. In this case flight may continue at the
discretion of the pilot, noting that falling voltage will eventually cause on-board electrical
systems to fail.
An optional external charging point is provided under the rear of the engine cowl with a
magnetic attachment to the supply cable. Trickle charge only, using the CTEK charger!
Fuses
Fuse description
Rating
Protects
Fuse type
Location
Main
incoming
supply to cockpit
30A
Main positive supply is
fed to the starter solenoid
from the battery. The
supply continues then
through the 30amp fuse
to the cabin.
Bolt in strip type,
MTA
S.p.A.
“Midival” range
Engine bay fuse box,
above left fuel tank, on rear
face of enclosure or engine
bearer.
Compressor
10A
Fuse only supplies the
pneumatic compressor
Automotive
Inst. Panel
Primary
Fuel
pump
5A
Fuel pump
Automotive
Inst. Panel
Secondary fuel
pump
5A
Fuel pump
Automotive
Inst. Panel
914UL TCU
5A
Engine control unit
Automotive
Inst. Panel