Radar altimeter not working
- Thread starter pstan
- Start date
JeffDG
Touchdown! Greaser!
Cat I, you're fine...Cat II or Cat III would become Cat I
HPNPilot1200
En-Route
Yes. Radar altimeter is not required for CAT I. In fact if you have one it is advisory only for a CAT I ILS since you fly the approach to a DA not a DH.
From Av Herald, http://avherald.com/h?article=44bfed8f&opt=0
pasted below is the pertinent portion
"the ground the crew determined a Category I approach (DH 200 feet AGL, minimum RVR of 550 meters required) was possible, advised tower accordingly also stating that they would divert to Lille (France) in case of another go-around.
When the aircraft descended through 1700 feet MSL the radio altimeter again began to function intermittently only, the crew continued the approach with the autopilot connected. Below 700 feet radar altimeter 1 failed to provide any height, the pitch angle started to oscillate, when the aircraft descended through decision height the pitch angle was 0.3 degrees, quickly increased to 1.3 degrees nose up before the pitch angle reduced by about 7 degrees. At about 120 feet AGL, the aircraft was already one dot below glideslope, the captain disconnected the autopilot and continued the landing manually in view of the approach lights and landed on runway 08R without further incident.
France's Bureau d’Enquetes et d’Analyses (BEA) released their final report in French concluding the probable cause of the incident was:
At the time of the occurrence the comparism of the height values displayed on the primary flight displays of either flight crew made it possible to detect the problem of radar altimeter #1. However, both flight crew were not aware of the consequences of how the autopilot would use those values, that the autopilot considered valid and thus tended to over-correct deviations of the ILS glidepath. While keeping the autopilot/flight director connected as long as possible the pilot flying was certainly surprised by the deviation from the trajectory and had to react at very low height to catch the glideslope and continue the planned descent."
Just some food for thought
Stan
pasted below is the pertinent portion
"the ground the crew determined a Category I approach (DH 200 feet AGL, minimum RVR of 550 meters required) was possible, advised tower accordingly also stating that they would divert to Lille (France) in case of another go-around.
When the aircraft descended through 1700 feet MSL the radio altimeter again began to function intermittently only, the crew continued the approach with the autopilot connected. Below 700 feet radar altimeter 1 failed to provide any height, the pitch angle started to oscillate, when the aircraft descended through decision height the pitch angle was 0.3 degrees, quickly increased to 1.3 degrees nose up before the pitch angle reduced by about 7 degrees. At about 120 feet AGL, the aircraft was already one dot below glideslope, the captain disconnected the autopilot and continued the landing manually in view of the approach lights and landed on runway 08R without further incident.
France's Bureau d’Enquetes et d’Analyses (BEA) released their final report in French concluding the probable cause of the incident was:
At the time of the occurrence the comparism of the height values displayed on the primary flight displays of either flight crew made it possible to detect the problem of radar altimeter #1. However, both flight crew were not aware of the consequences of how the autopilot would use those values, that the autopilot considered valid and thus tended to over-correct deviations of the ILS glidepath. While keeping the autopilot/flight director connected as long as possible the pilot flying was certainly surprised by the deviation from the trajectory and had to react at very low height to catch the glideslope and continue the planned descent."
Just some food for thought
Stan
poadeleted20
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Then I guess the real answer is "turn the radalt off and continue the approach to Cat I mins."
Piloto
Line Up and Wait
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Piloto
Some radar altimeters are better than others when flying over terrain with poor reflectivity. This could also be annoying if there is a parallel road to the approach with a lot of car traffic. Cars have high reflectivity that causes erratic readings. Heavy precipitation sometimes causes altitude readings at higher altitudes, sometimes activating the TAWS alarm. Very important also is to keep the radar altimeter antennas clean. If they are dirty and the terrain has poor reflectivity you may not get altitude reading.
José
José