How come selecting LNAV and HDG SEL change the vertical deviation i though VNAV would?

 

The FMC, like all computers is only as good as the programming and input. If you're in HDG SEL, the VNAV doesn't know what route you'll take to get on the glide slope. It assumes you're somewhere on final. I'm not 100% sure where that is. But, it isn't taking your heading into account as you can be on an intercept heading at a "good" altitude and the VNAV will think you are high.

 

If you then select LNAV while wings level on an intercept heading, the FMC can then figure out your routing and give you an accurate VNAV picture. The error between HDG SEL and VNAV decreases as you approach the FINAL APPROACH COURSE.

 

Basically, in HDG SEL the FMC thinks you are closer to the course than your actually are. LNAV does a better job of figuring our your route and therefore distance and therefore VNAV.

 

Also, when would you start the APU for engine start?

 

The APU takes about 50sec to spool up and then you need 1min to stabilize the APU before you can turn on the bleed. So, a minimum of 1min50sec. I'll usually start it about 5-10min prior to push unless there is a need for air conditioning. Then its when the FAs tell you they are hot or cold.

 

 

Then its when the FAs tell you they are hot or cold.

 

Which is pretty much always the moment they set foot on the airplane. 

Matt C

 

I'm doing an RNAV APP, i want to set RNP (0.30nm) on prog page 4 of the FMC how is it done?

 

also if i'm monotoring RAW DATA i tune the VOR but i don't inhibit the vor in the nav options is that correct?

Also for the RNP requirements RNAV 0.5nm and GPS  0.3nm 

 

what is the difference? i thought RNAV is GPS.....

 

 

I'm doing an RNAV APP, i want to set RNP (0.30nm) on prog page 4 of the FMC how is it done?

 

LEGS 6L is where I do it. You might be able to do in on the PROG page.

also if i'm monotoring RAW DATA i tune the VOR but i don't inhibit the vor in the nav options is that correct?

 

We don't inhibit VOR normally. We inhibit DMU update by default. So I'd say you are correct.

 

 

 

what is the difference? i thought RNAV is GPS.....

 

GPS can be RNAV, but not all RNAV is GPS. RNAV could be LORAN, INS, IRS, OMEGA, etc.

 

 

GPS can be RNAV, but not all RNAV is GPS. RNAV could be LORAN, INS, IRS, OMEGA, etc.

 

My first RNAV used VOR and VOR OFFSET.... it was very clumsy but you could draw a straight line on a sectional and then measure the radial and distance to each VOR you bypassed. Input that information into a box and voila you had Random Navigation!  They changed the name after that and the rest is history.

I read the name GPS is not longer used but now its RNAV (GNSS) also LORAN and OMEGA are very old and not used.

 

I found this

 

Well from our newly updated operations manual :

 

 

RNAV (GNSS) APPROACHES

 

 

Definition : non-precision approaches with LNAV or LNAV/VNAV minima.

 

 

- "RNAV (GNSS) approaches" corresponds to "RNP APCH operations"

 

 

- "RNAV (RNP) approaches" corresponds to "RNP AR APCH operations"

 

 

RNP AR OPERATIONS

 

 

General

 

 

Required navigation performance instrument approach procedures with authorisation required (RNP AR) are charted as RNAV (RNP) RWY XX " and contain a special note on the chart to aircrew and operators. These procedures are commonly referred to as "RNP AR" or in the USA "RNP SAAAR".

 

 

Can someone tell me what RNP you require for both of these?

 

Thanks.

My first RNAV used VOR and VOR OFFSET.... it was very clumsy but you could draw a straight line on a sectional and then measure the radial and distance to each VOR you bypassed. Input that information into a box and voila you had Random Navigation!  They changed the name after that and the rest is history.

In this case would you inhibit the GPS update on the 737? But RNAV VOR is also the thing of the past can't find much of those about.

My first RNAV used VOR and VOR OFFSET.... it was very clumsy but you could draw a straight line on a sectional and then measure the radial and distance to each VOR you bypassed. Input that information into a box and voila you had Random Navigation! They changed the name after that and the rest is history.

Ah! I'll bet you are referring to the Bendix-King KLN 80. An amazing system for its era. I installed quite a few of them back in the early-mid 1980s. You probably are be familiar with the gridded RNAV enroute charts that both Jeppesen and NOS used to publish, making it easier to plot a linear course and find bearing/distance offsets for VOR/DME stations along the route. I don't know if those charts are still available - probably not.

 

That was about the time that the first aviation LORAN units came to market, which soon became extremely popular in the GA world.

 

Though few Loran models were ever certified for "official" IFR enroute use, they were so much easier to use than a rho/theta RNAV, that sales of the KLN 80 went into the tank, and the model was discontinued.

 

And, of course, Loran itself was rapidly supplanted by GPS in the 1990s onward, and since the U.S. Loran system was de-commissioned a few years ago, any old Loran navigators still installed in are now just "gap fillers" in an aircraft's radio stack.

 

At least a KLN 80 would still work today, assuming the internal circuitry has not failed with the passage of time. I still see them once in awhile in older GA aircraft. The only problem with making the national airspace system almost totally dependent on space-based GPS, is what happens if the GPS satellites are damaged by a massive solar flare? In that case, old KLN 80s that still work might become worth their weight in gold...

 

 

what happens if the GPS satellites are damaged by a massive solar flare?

 

That keeps military planners up at night.  GPS must be the best civilian adoption of a military technology since interstate highways. I believe the planners plan survivability models based on the number of transponders in the constellation. You have to knock out quite a few to start having an operational impact.

 

Yes, I remember the KLN 80! And in fact we did migrate to the LORAN and after many years the TSO'd Garmins 530's became a necessity. I guess the next big thing is going to be ADS-B, which is already getting a lot of attention in parts of the world that don't have radar coverage.

In this case would you inhibit the GPS update on the 737? But RNAV VOR is also the thing of the past can't find much of those about.

 

He's talking about an older system that the NG doesn't use, so it's N/A. The NG does use VOR for its position data, so you are in a way VOR RNAV. Of course there are other inputs that go into the MMR.

Our policy is to disable the VOR updating on all approaches that are not an ILS.

Our policy is to disable the VOR updating on all approaches that are not an ILS.

Yes thats what i read on pprune a few days ago. you shouldn't need vor or dme updating for any RNAV (GNSS) OR RNAV AR app

 

 RNAV (RNP): Radios: Inhibit all VOR & DME updating from NAV OPTIONS page 2 prior to IAF

 

Joe diamond, so if thats the case you don't need to tune any VOR or NDB for any RNAV app, for raw data monitoring only for -  VOR, LOC, LDA, SDF, NDB, LOC BC ?

Yes thats what i read on pprune a few days ago. you shouldn't need vor or dme updating for any RNAV (GNSS) OR RNAV AR app

 

RNAV (RNP): Radios: Inhibit all VOR & DME updating from NAV OPTIONS page 2 prior to IAF

 

Joe diamond, so if thats the case you don't need to tune any VOR or NDB for any RNAV app, for raw data monitoring only for - VOR, LOC, LDA, SDF, NDB, LOC BC ?

Updating is only for the FMC positioning. That's completely separate from what you're doing with the NAV radios and CRS selectors in the cockpit. Inhibit doesn't affect what you see on the RMI or ND.

Yeh matt i'm clear with that thanks, just got my head around on all this!

 

Is there a need to monitor raw data on RNAV APP? Or do you still tune in any VORs that are available...

Yes thats what i read on pprune a few days ago. you shouldn't need vor or dme updating for any RNAV (GNSS) OR RNAV AR app

 

 RNAV (RNP): Radios: Inhibit all VOR & DME updating from NAV OPTIONS page 2 prior to IAF

 

Joe diamond, so if thats the case you don't need to tune any VOR or NDB for any RNAV app, for raw data monitoring only for -  VOR, LOC, LDA, SDF, NDB, LOC BC ?

 

We only need to monitor raw data if it's a non-overlay approach.  If the chart has "GPS" in the title it's an overlay approach and raw data does not need to be monitored.  A chart titled "VOR Rwy 36" requires the VOR to be tuned and monitored.  A chart titled "VOR or GPS Rwy 36" does not.  The VOR does not even need to be operational to shoot that approach.  It's pretty rare these days to have to monitor the raw data.  I can't think of the last time I actually had to do it.