Message Name:

WEATHER RADAR WEAK OR INCORRECT RETURNS

Weather Radar Receiver/Transmitter Antenna (RTA) does not provide expected weather information returns when there is no failure reported. This condition may be considered as weak or no target displayed, where weather depiction is expected.
OR
May be defined as incorrect/false target displayed.

NOTE: Replacing RTA without performing troubleshooting recommendations may result a No Fault Founds (NFF) situation at the repair facility.

• Radome
• Weather Radar Receiver/Transmitter and Antenna (RTA) (A125)

Advisory Wire/Service Bulletin:

• AW700-34-0166 - Update - Weather Radar Increased Ground Clutter During Flight
• AW700-34-0653 - Primus Weather Radar Altitude Compensated Tilt Control

Forum Articles/Infoservice/Newsletter:

• antenna plate inspection criteria - Honeywell System Description And Installation Manual
• WU880-A23-2000-018R002 - Honeywell Troubleshooting Guide for Airborne Weather Radar

1. Flight crew should be familiar with the Honeywell Primus 880 WXR_PG_A28-1146-102-r004 for optimizing radar performance.
2. Incorrect repair procedures or thickness of paints affects radome performance. Therefore, it is important to identify the problems reported by the crew whether the radome was under proper maintenance activities before any troubleshooting.
3. Ice/water inside the radome or trapped within its walls does not generally cause radar hard failure, but it may affect it's operation. The radome is constructed of materials that allows the radar energy to pass through with little attenuation. Ice/water increases the attenuation and decreases sensitivity of radar signal. Ice can cause refractive distortion; a condition characterized as loss of image or blind spots definition. Ice also creates reverberant echoes within the radome, this condition might be indicated appearance of non existing targets.
4. The radome can also cause refractive distortion making the TILT control appears to be out of adjustment, or bearing indications appear to be erroneous.
5. If a target changes significantly in size, shape, or intensity as aircraft heading or attitude changes, the radome is probably the cause affecting this condition.
6. Significant damage to the antenna flat plate radiator may affect radar display. When there is a rise in the level of the side lobes generated by those damages, false targets or target smearing will appear on the radar display.
7. Some Operators reported water accumulation in the radome area during heavy rain, even with proper performance of the seal. It was identified that the water was actually coming from the TRU bay area via opening between TRU bay and radome area. Mod sum IS700-52-0002 was developed to improve the water tightness of the TRU electrical bay doors. Performance of radome and TRU doors seals can be checked by water spray test.

NOTE: This Mod sum is NOT posted on CIC Website and will be made available via SRPSA only, please contact Customer Response Center for further information (Kit drawing KGC991-1215 (A/C 9140-9999) and KGC991-1214 (A/C 9002-9139)).

1. Ensure that there is no failure when performing the weather radar operational test.

   1. If any fail code is present, troubleshoot the condition first. With the aircraft outside the hangar and with proper clearance in front of the aircraft, align the IRS on ATT mode, calibrated gain and select the system to WX. Monitor the radar returns at different tilt values (make sure that tilt works correctly by monitoring the displayed value) and monitor for any abnormal condition.
   2. If system checks are good, continue with next step.
      NOTE: To evaluate a basic radome performance, locate a target few miles away (i.e. antenna, tower, building) and record the level (color) at which the return occurs. Then open the radome and record the return (color) levels of that same target. If the intensity color/level goes way up it may be an indication of a radome problem.

2. Select radar to OFF (on both Controllers) to perform a visual inspection of the external portion radome.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

3. Perform radome external visual check for damage of the outer surface of the radome. For allowable damage, refer to SRM 53-60-01. Damage area may be of concerns as they may be the entry point of moisture within the interior wall.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.
      NOTE: Perform a tap test. Using a small metallic object, tap lightly on the radome surface and listen to the noise it generates. If you get a dull "thud" sound it may be an indication of a radome inner layers damage and moisture absorption (ice when at altitudes) zone, that affecting the radar.

4. Check condition of the nose erosion boot if installed. Moisture may be trapped between the cap and the radome, that affecting the radar.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

5. Perform general condition check and bonding/resistance test of static diverter strips. Refer to SRM 53-60-01 for allowable damage and test values.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

6. Open the radome and perform visual inspection of the internal portion of the radome and RTA.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

7. Perform RTA visual check. Make a visual check of the RTA external surfaces for possible damage. Check air vents and external connectors for dust, corrosion, or damage.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

8. Check external parts for loose or damaged hardware.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.

9. Check the flat plate antenna for severe damage due to dents, pinholes, or warps.

   1. If there is any damage, repair as required and do close out.
   2. If there is no damage, continue with next step.
      NOTE: The following are general guidelines when checking for damage (for more details refer to the Honeywell SDIM for antenna plate inspection criteria (section 3-8):

   • A single dent is less than 1/16 inch in depth. A dent deeper than 1/16 inch or multiple dents may cause a degradation of side lobes
   • A pinhole is less than 1/16 inch diameter anywhere on the face of the flat plate
   • Warping of the flat plate is less than 1/8 inch

10. Perform radome internal surface visual check. Check for any signs of excessive moisture on the antenna, the interior wall of the radome or accumulated water at the lower section of the radome.

    1. If moisture is found, verify seal and latches for proper operation (this can be done by spaying water on the closed radome and TRU bay doors and then monitor for any water ingress). As required, evaluate incorporating IS Mod sum IS700-52-0002.
    2. If NO, continue with next step.
       NOTE: This Mod sum is NOT posted on CIC Website and will be made available via SRPSA only, please contact Customer Response Center for further information.

11. Check for damage to the inner surface of the radome.

    1. If there is any damage, repair as required and do close out.
    2. If there is no damage, continue with next step.
       NOTE: Tap test can be used. In addition, pay attention to darker areas, they may be a sign of inner layers damage and moisture absorption zone that affecting the radar.

12. If the above steps do not show any problem, the radome may still be a possible cause. Then the only way to guarantee radome performance is a bench test called transmitivity check per RTCA/DO-213 for Class A.
    NOTE: Some specialized facilities are able to perform this bench test in a single day if organized in advance (Contact your local Bombardier service facility or ASF for assistance). Another radome can be installed for troubleshooting if available. Since this is a complex process, operator may elect to simply replace a RTA for troubleshooting. If there is no improvement after a RTA is replaced, it is important to focus on troubleshooting the radome.
    NOTE: Replacing RTA without performing troubleshooting recommendations may result a No Fault Founds (NFF) situation at the repair facility. Please indicate details in the RTA removal documentation.
13. Do close out.