SPZ-7600 ILS problem
Hi All,
We are encountering a problem when flying ILS approach. The glideslope deviation fluctuates randomly; for a while the R/C is exactly on the correct glidepath and then suddenly the R/C starts to deviate and the corrective action seems to be really slow, althought the pitch command indicator on ADI shows correct attempt to restore the optimum path. Flying several ILS approaches in sequence does not reveal any regular pattern, but sometimes we are within 0.5 dot through the whole glide and then sometimes more than 1 dot off especially under 500 ft where the glide path gets narrower. This R/C has dual FD, 3-axis, SPZ-7600 autopilots.
The ILS signal is received correctly, without flags. Pilots say that with reference to PAPI the GS indication on EHSI is correct.The R/C performs autolevelling correctly, so the radar altimeter is functioning for GS gain programming.
The airdata system has some small fluctuation in vertical rate (inside 25ft per minute) and the autopilot calculated TAS is slightly smaller than expected (2-4 kts), but still these errors are quite small and not considered as causing this issue completely. Basically, it feels that the autopilot is just slow on pitch channel!
Does anyone know what kind of registers there are that could be used to monitor autopilot pitch channel gain? Are there any adjustable gain settings on pitch channel or some adjustable pitch rate settings?
How to test that the pitch jackscrew actuator has the needed speed&response to keep the R/C at correct glideslope?
Thank you in advance,
Karote