SIN No. 2673-S-28
SUBJECT: FUEL SYSTEM
Information concerning LOW FUEL warning
Applicability EC135 T1, T2, T2+, P1, P2, P2+, 635 T1, 635 T2+, 635 P2+ MBB BK117 C-2
Eurocopter has been informed by Bond of an issue involving the fuel indication system on one of its
EC135 EMS aircraft during normal operation. Following this incident, tests performed on EC135 have
revealed supply-tank fuel gauging errors on some aircraft.
The first analysis shows that the indication of the fuel quantity in the supply tanks could be
overestimated. All crews should be aware that in the worst case a red warning LOW FUEL 1/2 could
appear without any amber FUEL caution before.
The red LOW FUEL 1/2 warnings are generated by an independent switching logic with separate
sensors in each supply tank. The red LOW FUEL 1/2 warning lights continue to operate correctly
even if the fuel gauging is inaccurate.
Therefore we want to remind you that:
• After illumination of LOW FUEL warnings the procedure iaw. the Flight Manual must be strictly
complied with, notwithstanding of the fuel quantity indication.
In addition we want draw attention to the proper airmanship iaw. Air Ops NCC.OP.131 “Fuel and oil
supply — helicopters” and NCC.OP.205 “In-flight fuel management” to ensure situational awareness
concerning fuel usage and flight time left.
Furthermore, we want to remind you of Information Notice 2535-I-28 “Notes about possible water
contamination of the fuel system”.
SIN No. 2535-I-28
SUBJECT: FUEL SYSTEM
Water contamination of the Fuel System
Applicability EC135 T1, T2, T2+, P1, P2, P2+, 635 T1, 635 T2+, 635 P2+ MBB BK117 C-2
EUROCOPTER has been informed about several fuel quantity indication failures. Following the
replacement of the affected fuel probe, the indication returned to normal and the functional check of the
fuel quantity indication system has been performed successfully.
When the subject probes have been returned to EUROCOPTER for repair, the probes showed no
external damage or contamination within the two concentric metal tubes and most of the probes have
been tested, with the result, “no fault found” (NFF). To investigate the reason for these NFF’s
EUROCOPTER performed several tests to simulate the failures. As a result from these tests, the most
probable root cause is contamination of the fuel probe with water.
These tests have shown - when water is entering the space between the two concentric metal tubes of
the probe - it will decrease the output signal (frequency) of the probe. In case of a high concentration of
water, the frequency can decrease to such a level that the CAD recognizes the probe as failed –
showing either an F QTY DEGR or F QTY FAIL caution on the CAD. Also there is a potential risk that the
CAD shows a higher fuel quantity level compared to the actual fuel level within the fuel tank system.
In addition, customers have reported, when removing the defective sensor from the helicopter, that after
removing the water by the use of shop air and warming up the sensor for a certain period of time, the
sensor has been working again without any fault.
It should be noted that even for operators that regularly drain the fuel tanks, a couple drops of water
concentrated between the metal tubes of the sensor may be enough to affect the signal.
There are several possibilities for the fuel system to be contaminated with water:
· Condensation within the fuel tank system. This is mainly caused when the fuel tanks are not
completely filled and the helicopter is parked outside and/or is exposed to great changes in
temperature
· Heavy rain during refueling of the helicopter – water is entering through the filler neck
· Contaminated fuel from the source – for example fuel truck, tank, supply system or barrels
· For EC135 when performing an engine compressor wash, the water from the combustion
chamber is drained into the drain bottle. On some helicopters there is a chance that water from
the drain bottle is sucked into the engine fuel system via the Fuel Control Unit. Operating the
prime pumps prior to the next engine start will allow the water to enter the helicopter fuel system
through the fuel return line and the fuel expansion box. From the fuel tank expansion box the
water will then flow back into the RH Supply Tank.
Therefore, as explained in the AMM Task 71-65-00, 7-1, it is recommended to follow the procedure and
to disconnect the combustion chamber drain tube before prior to starting the compressor wash process.
Due to the reason mentioned above, EUROCOPTER wants to point out the importance of keeping the
fuel system free of water and other contamination. When draining the fuel system, in reference to the
documents listed below, it must be performed before the helicopter is moved, in order to allow the
maximum amount of water to be drained from the tank.
EC135
AMM, Chapter 12-30-00, 3-5
MSM, Chapter 05-25-00, 6-1
FLM, Section 4 – Preflight Check
FLM, Section 8.3 – Drainage Procedure
BK117C-2
AMM Chapter 12-30-00, 3-16
MSM, Chapter 05-25-00, 6-1
FLM, Section 4 – Preflight Check
FLM, Section 8.3 – Drainage Procedure
In addition EUROCOPTER wants to point out that water – if not drained from the fuel system – can
cause different malfunctions within the fuel and engine system.
If there is doubt that the fuel system is free of water, EUROCOPTER recommends to take a fuel sample
from the helicopter tank system and to test it for the presence of water by using commercially available
Test Strips, for example the SHELL Water Detectors or another commercially available product.
Last edited by RVDT; 16th Dec 2013 at 19:02.
Reason: IN Number corrected