The Aspen also provides baro-corrected altitude in its 429 bus air data stream, which in my installation is transmitted to the GTN750. I dont know if and how such data is used by the GTN.
If you have baro-corrected altitude, you do not need to know pressure altitude or altimeter setting to figure a glideslope. BTW those two are also provided in the same data stream:
+V is only for lnav 2d approach I think, it’s just a gift for reducing worload during final.
When you have Baro vnav, it’s different approach called “abas” or lnav-vnav, (airborne based augmentation system), which cross-check GPS altitude with Barosetting. It’s less precise than sbas or gbas but better than just lnav in terms or minima. And for this approach you have to use lnav+vnav minima.
I don’t think that we are talking about Baro-VNAV approaches here. They are certified and need certified equipment and training.
We are talking about how barometric input may be used to enhance the uncertified +V assistance.
Originally we were talking about the effect of switching off SBAS in training to emulate a 2D approach, then non-SBAS environments were introduced to explain why GPs are provided when SBAS is unavailable or switched off.
In non-SBAS environments, there are Baro-VNAV approaches, but they cannot be flown with non-certified equipment except as LNAV, to LNAV minima. The GTN will probably provide a slope, but it will be an uncertified +V.
So Baro-VNAV is not really part of the discussion.
SOP in an ATO is NOT to disable SBAS. PBN training requires that student understands when a GNSS RNAV is 2D or 3D, and use appropriate technique and call outs.
Thank you for the interesting discussion from my OP – it does rather start to resemble a monty python skit when you start to get further into the detail! I’m forever thankful for the excellent PPLIR reference book when instructing this stuff… I will also ask some senior IREs I know via our examiner forum what they think/know about disabling the +V…
I’m forever thankful for the excellent PPLIR reference book when instructing this stuff
Thank you, but this particular aspect is not covered, or even thought about, in the Manual.
My view is that how to disable stuff for training purposes is outside scope (please shout if you disagree) but there are definitely statements in there that SBAS is required for 3D and it does seem that technology is overtaking that position, so I must make carefully nuanced adjustments.
I really don’t want the book to be about how particular versions of software in particular boxes work, but equally what it does say must be correct, obviously.
That is why I must investigate this more fully before going to print.
Timothy – totally agree the content is pitched right
In my simple mind, I think of a hierarchy of:
Groundschool Reference – detailed technical notes / reading for reference (PPLIR manual pitched here?)
SOPs – type and organisation specific, standardised way how to fly/do stuff
Training Manual – possibly type and organisation specific but could be generic, how to teach something with lesson objectives etc..
Student Notes / Guide – reading for the airborne / ground training
I would say the disabling of functionality for training is an issue for organisation SOPs and Training Manuals
Timothy,
As far as I know, disabling the SBAS or selecting a particular SBAS to be enabled/disabled is pretty much a standard function. So there is some useful general knowledge to be understood when SBAS is disabled.Examples include: affects on integrity and requirements for using RAIM, potential training uses, annunciations, and disabling adjacent SBAS systems, recognizing when not receiving SBAS …
Those are all covered except the training uses of disabling SBAS.
I flew today. Disabling SBAS at my airport, GTN750 SW 6.62, the RNAV approaches annunciated LNAV+V. Turned SBAS back on and the system annunciates LPV for the same approaches. Timothy, I took pictures if you are interested.
