Today I flew from EGKK to TXKF and had a problem manually tuning the NAV1 radio.For approach I had to use runway 12 VOR/DME approach rather than the preferred ILS runway 30. No problem, got the chart, flicked the switch to MAN and tuned in the BDA VOR at 113.90. Continuing my approach I look up to see the button back at AUTO and my VOR tuning is gone...no luck when I switched back to MAN as it is also tuning in the ILS. So I decide to tune via FMC and enter BDA into the VORL, sure enough it shows BDA 113.90 M so we are all set. On final approach 10 miles out, I lose it again and I was not visual yet...minor panic!!! Anyway got it tuned again via MAN button on MCP and nailed the landing without any of the PAX realizing the peril they were in, but I don't understand why that happened. Any advise.Mark.

"The ILS frequency and course for the runway selected in the FMC is automatically tunedinto the NAV1 receiver when approaching the arrival airport provided the receiver is placedin the AUTO mode. This feature did not work 100% of the time depending on the methodof runway selection. This update makes the ILS auto-tune capability work 100% reliablyprovided the NAV1 receiver is in the AUTO mode. Please see section 2.D for moreinformation on this feature.As a reminder, the ILS frequency that is auto tuned will change with the selection of anEHSI mode other than MAP or PLAN.When selecting an ILS or VOR EHSI display mode, theNAV1 receiver switches to MAN mode automatically. . If an ILS is tuned in and is beingtracked in the LOC mode, the LOC mode will fail unless the proper ILS frequency has alsobeen manually programmed. Therefore, during any ILS approach, it is a good idea tomanually tune the ILS frequency as well, just in case a different EHSI mode is required."ie:put the EHSI in VOR or ILS mode,and it should not happen(who needs maps anyway?;-) )...i can however be wrong,as i am now flying DC8's ;-)