Lufthansi From Germany, joined May 2002, 454 posts, RR: 2 Posted (5 years 5 months 5 days 19 hours ago) and read 7031 times:
I'm just doiung my (Maintenance Personel) Boeing 737CL Typerating.
Yesterday I had to write an exam about ATA 22 and ATA 34. I had a great success by having 31 right answers out of 33. One of the questions I answered wrong was about the ADF needle that can be shown on the EHSI (Electronic Horizontal Situation Indicator = lower display).
The question was: "What happens to the ADF needle on the EHSI when there is no reception on the selected ADF frequency"
a) it is not displayed
b) it is shown parked at the 09:00 o'clock position
c) it has no special position
Answer "b" was pointed out to be correct by two instructors. I've choosen "a" though...
I'm very sure that the needle is not displayed anymore.
It's clear that on the RDDMI the needle would be in the parked position ( 09:00 o'clock) since it cannot be removed on an analogue instrument.
But from my experience on the 737 of Lufthansa and my 737PIC I use to fly on my flightsim it is not shown if no frequency (within the range of reception) is selected.
[Lufthansa has no ADF selectable on the RDDMI (only 2 VOR needles). But on my sim the 737s have the RDDMI where each needle can be used vor VOR or ADF display.] And in each mode (FULL VOR/ILS; EXP VOR/ILS; etc) the ADF needle disappears if an ADF FREQ wihout reception is selected.
According to the instructor only on the 737NG and A320Fam. (talking about short range aircrafts here...) ADF needles are removed from the displayes when there is no reception.
Hence the course will be running for more than a week from now I don't have the time to jump into on of our Bobbies. So your experience is highly welcome!
WILCO 737 has a great image up here for this discussion. HSI is seen here and the RDDMI is pointing out 2 VOR/DME stations (no ADF selectors on LH 737s!).
ChrisMUC From Germany, joined Jul 2006, 66 posts, RR: 0
Reply 1, posted (5 years 5 months 5 days 2 hours ago) and read 6951 times:
I had a quick look into my documents (OM-B, Chap. 12.11.30) to check (didn't want to rely on my memory) and you're right. On page 1 is stated that in case of ADF receiver failure the pointers are removed and on page 8, what is your question, that the pointer is only displayed if an ADF bearing is being received.
That's also what I remembered from flying the Bobby.
Avt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 3, posted (5 years 5 months 3 days 19 hours ago) and read 6848 times:
I would choose "a" as well, based on my knowledge of other EFIS aircraft. I'd be curious to know if "ADF failure" and "no reception" are the same thing, and handled the same by the system. I know of a case where DME failure, and DME weak/no signal are displayed differerntly.