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737NG-FTD-34-09001 ATA: 3433-00 Last Revised: 11-FEB-2009
Issue Title: LRRA Flags and Warnings Originated: 11-FEB-2009
Airplane Model: 737NG Minor Model(s): -600, -700, -700C, -800, -900, -900ER, -BBJ Other Models:
no other models applied to issue ECD: 23-SEP-2009
Illustrations:
References:
Fleet Team Resolution Process Item (FTRP) 03674-737
Issue Status:
Open
Description
Boeing has received numerous reports related to discrepant radio altimeter system operation. Typical symptoms include the appearance of the RA Flag, Landing Gear Configuration Warnings, negative altitude values displayed while the airplane is in cruise or above 2,500 feet, and, more recently, autopilot disconnects on approach. Troubleshooting using the DFCS and/or PSEU BITE may find fault codes related to the radio altimeter.
For many reports to date, the system works as expected most of the time but experiences intermittent flags and warnings. The reports may be common across a fleet of airplanes and may not be limited to one or two airplanes in a given fleet.
Available data suggests the causal factors are related to moisture control and accumulation. Boeing’s current recommendations include making sure the fuselage bilge drain valves function properly per AMM 51-41-11/601 and that operators may want to begin periodic inspection of the antennas to check for signs of moisture ingress and corrosion.
Status
Boeing is seeking operator experience with regard to LRRA anomalies as outlined above. Please provide feedback to the questions in the "Operator Action" section.
Interim Action
Boeing offers a No Technical Objection (NTO) to use Aviation Devices and Electronic Components LLC (Av-DEC) Connector Wrap, part number EN110589-01, as an optional application around the radio altimeter antenna connector/coax cable installation to reduce any moisture effects. Contact Boeing Service Engineering if more details are needed.
Av-DEC’s contact information is as follows:
Aviation Devices and Electronic Components LLC
1810 Mony Street
Fort Worth, Texas 76102
Phone: 817.738.9161
Fax: 817.738.9163
Email: info@avdec.com
Boeing suggests that if the connector wrap is used, the antennas also be replaced with new antennas to establish a known baseline.
Final Action
Final action will be determined from the data gathered from this and other ongoing efforts.
Operator Action
Boeing is seeking operator experience with regard to LRRA anomalies as outlined above. Please provide feedback to the following questions on this posting:
1. Does the number of radio altimeter system reports vary by season? That is, wet versus dry season, summer versus winter, etc.
2. Are there signs of moisture or corrosion underneath removed antennas thought to be causing problems?
3. GPWS discrepancies are sometimes reported along with the radio altimeter system issues. Do other airplane systems indicate problems while the radio altimeter is acting up? Which systems? What symptoms do these systems show?
4. For those operators that have used Av-DEC Connector Wrap on the radio altimeter antenna connectors as a barrier to moisture intrusion, did the application improve system reliability or operation?
5. Boeing is interested in studying radio altimeter antennas with visible corrosion or moisture effects. Any antennas sent to Boeing may be dismantled in the course of the investigation, so only parts that may be scrapped should be sent to Boeing. Contact your respective Boeing Field Service Representative or Service Engineering via normal business channels for shipping address information.
Responses to these questions and any other observations may be posted in the FTRP Bulletin Board, item 3674.
Affected Documents
FTRP Bulletin Board Item 3674
Parts List:
Part Name: Boeing Part Number: Supplier Name: Supplier Part Number:
LRRA Transceiver
Honeywell
066-50007-0101/-0111
LRRA Transceiver
Collins
822-0334-002/-003
LRRA Transceiver
Thales
9599-607-19993
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发表于 2009-3-6 23:52:49
