Again on 172SP 2003 Bandix/King GPS unit. On this plane there is no separate DME stack so I have to use DME on GPS it self. For example, I know that I need to plug in LAX instead of KLAX and reference distance from LAX to shoot the approach, get MAP or/and stepdown fix since it's VOR distance that's referenced rather than airport.

Having said, I have two questions.

-When I dial in VOR Identifier on GPS to use as DME, it takes rather longer time than planes with DME stack it self. What I mean is on Bandix/King, I have to click "direct" then use two knobs to set the alphabets and click enter twice in order to activate. However on older DME unit, you just tune the frequency and it's activated. I know it's only couple seconds of difference but I think couple second in IMC is pretty significant. So my questions is, are there easier or quicker way to dial in VOR station on this model GPS that I'm missing out?

So to clearify, this is what I do. EXample, Click "direct" dial in "LAX", click "Enter" "Enter".

-When I plug in the airport rather than VOR, which part of airport is GPS measuring to? Is it center of runway?Airport?

Thanks!

 

Use the big knob and find the nearest page. Then small knob for nearest airport, vor, ndb, etc. (Trying to remember) but I beleive if you push the knob in you can select a waypoint and go direct from there. When you dial in a airport you are getting the distance from the airport referance waypoint (not always the center of the airport). At a large airport like KLAX it could be a signifigant distance from where the actual VOR is located.

 

Also, isn't GPS distance based on point to point whereas DME is slant range? Do GPS units now correct itself based on altitude?

 

GPS does not measure slant distance. It measures as if there is a vertical axis representing the waypoint from ground level to infinite height.

Using GPS for navaid substitutions will be easy if you have a non-GPS approved approach loaded as an advisory-only approach. This is a good practice to increase situational awareness. Load your advisory approach at the same time as setting up for the non-GPS approach, and if it is a second or third approach to the same airport you might do that during the missed approach legs. Any navaid for substitution would probably be already there. If not pull out the righthand knob, turn counterclockwise and you will get a list of the nearest 20 navaids. Do a direct-to the one you need for substitution. This will work best if the GPS is already up and running with at least the current destination in play, again this is a good practice to cultivate.

My instructor used to say use all your equipment. I kept that in mind until I got this one old airplane with a worn out Loran, wing leveler that thought a 5 degree bank was level, and a weak ADF.