Mark-1F glide slopes operate at 80 percent modulation. What was it for earlier versions i. e. Mark-1C, Mark-1D, etc.

  • 1
    $\begingroup$ By "Mark-1" you are likely referring to Wilcox Electrics Mark-1A, C, D and E and Eaton/AIL Mark-1B deployed by FAA in the US. ILS GS are expected to be compliant with ICAO Annex 10. To check whether the ICAO specifications changed, could you tell us the years these models were sold/deployed? 1B seems to be around 1980. $\endgroup$
    – mins
    Feb 14 '19 at 17:08
  • 1
    $\begingroup$ I think I figured out the answer, but won’t select it for a few days to allow input from others. $\endgroup$
    – Javelin
    Feb 17 '19 at 5:07

The percentage of modulation hasn’t changed, rather the way it is measured. Upon further review the current measurement is 80% SDM (sum), where before the measured value was 40% for 90 & 150 hertz individually. The method of measurement change, may be due to rare case instances where 90 and 150 shouldn’t be exactly equal, but together the sum is always 80%.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.