Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NM-08-10
December 7, 2007
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin alerts operators,
repair stations, mechanics holding Inspection Authorizations (IA),
Flight Standards District Offices (FSDO) Principal Maintenance
Inspectors (PMI) and/or Principal Avionics Inspectors (PAI) of service
difficulties and possible reliability problems associated with
potentiometers for EMBRAER Model EMB-120 airplanes.
Background
We have become aware of service problems concerning potentiometers
that provide information on the positions of the primary flight
controls to the flight data recorder (FDR). Electrical noise generated
by the potentiometers may result in the transmission of incomplete or
inaccurate data to the FDR.
EMBRAER has developed a procedure for detecting potentiometers with
noisy signals and ensuring that the potentiometers are properly
calibrated. We are also aware that the number of Model EMB-120
airplanes operating in the United States has decreased significantly.
In addition, the affected potentiometers (made by Penny & Giles)
are being replaced with MPC potentiometers via the Supplemental Type
Certificate process.
We have determined that while a noisy or improperly calibrated
potentiometer may hamper the ability to access certain aircraft data
recorded by the FDR, there is no direct effect on the aircraft’s
ability to be operated safely. Therefore, no unsafe condition is likely
to exist or develop on Model EMB-120 airplanes.
We consider reducing the likelihood that the potentiometers transmit
noisy signals or become improperly calibrated to be important. For this
reason, the information concerning EMBRAER’s procedure for reducing the
likelihood of noisy or improperly calibrated potentiometers should be
made available to affected owners and operators of Model EMB-120 series
airplanes. This action is needed to ensure that accurate data are
available to support an investigation in the event of an accident or
incident.
Recommendations
We recommend that you calibrate the potentiometers to the ailerons,
elevators, and rudder; perform a noise check of the potentiometers; and
obtain a readout of the FDR; in accordance with Section 31-30-00 of the
EMB-120 Airplane Maintenance Manual (AMM); and apply locktite adhesive
over the threads of the screws of the flexible couplers that attach the
shafts of the potentiometers to the shafts of the primary flight
controls, in accordance with EMBRAER Service Bulletin 120-31-0038.
Repeat the calibration and noise check at intervals not to exceed 6
months. If any readout of the FDR indicates a potentiometer with a
noisy signal, replace the potentiometer in accordance with Section
31-30-05 of the EMB-120 AMM.