Surely LNAV+V must be safer?

[Traffic_Is_Er_Was]

I chose "more than likely" because that is more than likely the outcome. The two jets at Mildura were both appropriately equipped, and both crewed by two experienced, current, instrument rated, CRM trained pilots, who knew what they were doing, and even then the Virgin aircraft only got in by the skin of its teeth. How do you think Joe Bloggs will go, especially if the terrain isn't "very flat"?

[werbil]

Originally Posted by alphacentauri

^^^^^THIS^^^^^^ Is the crux of 3 pages of discussion.

I've no issues with +V. The issue I have are the people who don't understand how it works.


Werbil, I have some questions regarding your post;



Did you have to set OAT on your equipment?
How do you know it was showing affects of temp...and not something else? (genuinely curious) Not trying to be a smart@rse, but I wasn't aware that +V took into account any temperature.

Questions for everybody.
1. Using +V with no external information sources where do you think the GPS gets altimeter information from? (I'll give you a hint it is not referenced to MSL)
2. Provided you know the answer to question 1, do you know what the difference between MSL and +V altimetry is? (Hint it is not a fixed number in Australia)

Can someone in Perth who uses +V tell us what the +V profile reads when doing RNAV approaches in SW WA?

Any survey lidar pilots on here? Has the GPS altitude for you lidar runs ever been the same as the barometric altitude shown on the altimeter? Is it different depending on whereabouts in Australia you are?

The GSL generated altitude by the GPS is completely independent of temperature and barometric pressure. The altimeter is affected by both both pressure and temperature from ISA - the QNH we set in the Kollsman window to allow for pressure error, the temperature is not adjusted so the altimeter is not corrected. Allow 4% per 10 degrees variation from ISA - so starting the approach at 3'000AGL , at ISA+15 you will be approximately 180 feet higher than what the altimeter reads.

When you keep the glide slope centered fly using +V guidance, you can see the delta between generated glideslope and profile altitudes reducing the closer you get to the runway - obviously complying with the descent step limits. The temperature error is noticeable on the ILS at the OM - I brief to expect to see a difference, which is definitely noticeable.

There is a reason that TAWS-A uses GSL altitude and a Rad Alt rather than barometric altitude.

[werbil]

I think that Dick is on the money with this one.

I saw a similar slide to this on my CFIT course. Until you see the data, it's pretty hard to believe that if you're going to CFIT on a non precision approach in all likelihood you'll be aligned with the runway.

[LeadSled]

Folks,
It is a great pity that it has become so unnecessarily expensive to establish instrument approach procedures in Australia, and the fact that quite a few long standing procedures have been forcibly withdrawn, when a bit of common sense would have allowed many to remain.
Tootle pip!!