ILS question re altimeter checks
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ILS question re altimeter checks
Refer to ENR 1.5 - page32. Sub para 7.3 ILS Altimeter checks.
I see that para 7.3.1 (a) states: To ensure obstacle clearance, both LLZ and glideslope should be maintained within half scale deflection (or equivalent on expanded scale).
In that case, if the normal LLZ deviation scale (737 EFIS for example) is one degree per dot, and the expanded scale is half a degree per dot, then it seems to me that that the expanded scale is not applicable when it comes to the obstacle clearance LLZ requirement stated in ENR 7.3.1 (a)?
To put it another way: if you are on the ILS and you are exactly half scale deflection on the LLZ normal scale (one degree per dot), the expanded scale would show the LLZ needle beyond or outside the limits of the expanded scale. Therefore there is no point to the ENR additional statement of: "or equivalent on expanded scale". - because there is no equivalent, is there?
Maybe I have read it all wrong of course, but any comments would be appreciated.
I see that para 7.3.1 (a) states: To ensure obstacle clearance, both LLZ and glideslope should be maintained within half scale deflection (or equivalent on expanded scale).
In that case, if the normal LLZ deviation scale (737 EFIS for example) is one degree per dot, and the expanded scale is half a degree per dot, then it seems to me that that the expanded scale is not applicable when it comes to the obstacle clearance LLZ requirement stated in ENR 7.3.1 (a)?
To put it another way: if you are on the ILS and you are exactly half scale deflection on the LLZ normal scale (one degree per dot), the expanded scale would show the LLZ needle beyond or outside the limits of the expanded scale. Therefore there is no point to the ENR additional statement of: "or equivalent on expanded scale". - because there is no equivalent, is there?
Maybe I have read it all wrong of course, but any comments would be appreciated.
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Firstly everyone please pardon my ignorance as I have no specific familiarity of the 737.
If the LLZ normal scale 1 dot is 4 times more sensative than the VOR (2deg) then 1 dot LLZ = 1/2 degree deviation, not 1 degree?
I think the expanded scale is the middle half of the scale, from half deviation each way of centre? So about 1.5 degrees to each side from centre approx...
More learned pilots and 737 drivers are free to correct me if in error.
Cheers!
Zhaadum.
If the LLZ normal scale 1 dot is 4 times more sensative than the VOR (2deg) then 1 dot LLZ = 1/2 degree deviation, not 1 degree?
I think the expanded scale is the middle half of the scale, from half deviation each way of centre? So about 1.5 degrees to each side from centre approx...
More learned pilots and 737 drivers are free to correct me if in error.
Cheers!
Zhaadum.
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As far as I recall the typical 737 EFIS LLZ normal display has two dots either side of the central datum while other types of nav sets show 4 dots either side - each one being a quarter of a degree.
Thus each dot on the 737 EFIS LLZ indicates one degree - not one quarter of a degree. That's what the manufacturer says, anyway.
Thus each dot on the 737 EFIS LLZ indicates one degree - not one quarter of a degree. That's what the manufacturer says, anyway.
In your example you say that normal scale is 1 degree per dot and that the expanded scale is 1/2 degree per dot.
Assuming that there are the same number of dots in both scales then the equivelent of 1/2 scale deflection would be full scale deflection. Make sense?
Assuming that there are the same number of dots in both scales then the equivelent of 1/2 scale deflection would be full scale deflection. Make sense?
