Can't capture ILS, aircraft just turn around at WSSS

[Zeke*Earl]

Hi All,

I tried performing an ILS landing on Singapore WSSS 2L (ILS 110.90), but as soon as hit the APP button, the aircraft just turns around like it was blind to the ILS frequency (110.90 was set in the FMC and i had also manually tuned 110.90 on the NAV dial). I did notice that VOR LOC was activated on the EFIS prior to the turn around. I haven't encountered this problem with the JAR A320 & A330.

Hope you guys can provide some insight. Thank you.

 

 

 

[Morten]

CRS set to runway heading?

[Zeke*Earl]

Oh no I did not set CRS. I assumed the FMC will automatically set it. Will try tonight when I get home from work. Thank you. 

Edited May 26, 2016 by Zeke*Earl

[Litjan]

Yeah, this one crops up all the time. Modern aircraft (even Boeing) will read the ILS front course from the FMC database and set up the AP to follow it upon LOC capture.

On the 737, the FMC is not linked to the NAV radios in any way. You have to set up both the frequency and the ILS front course. Front course information is not transmitted by the ILS, just a "fly left, fly right" information. So when the LOC is captured, the plane has NO IDEA where to turn initially, to keep the needles centered. It needs the ILS course to be able to turn onto it. After it does, it will adjust for drift (due to wind, for example). If you set up a SLIGHTLY wrong inbound course, the AP will able to compensate for that (it is the same as having a crosswind), but if the front course is grossly wrong, the AP will turn away from the LOC initially and totally run off it before it has a chance to adjust.

This is exactly like it is in the real plane (take it from someone who had to overpower the AP more than once because the plane turned away from the airport on LOC capture, because he forgot to set the inbound course )

Jan

 

[Zeke*Earl]

On May 26, 2016 at 9:55 AM, Zeke*Earl said:

Oh no I did not set CRS. I assumed the FMC will automatically set it. Will try tonight when I get home from work. Thank you. 

Setting CRS solved the problem. Thanks guys!!