Tuesday, December 14, 2010

SVS, huh? What is it good for?


“I don’t fly in the mountains, so I really don’t need synthetic vision.”

If I had a dollar…Yet I can’t blame the average pilot who has yet to experience SV for sharing this opinion.  The marketing materials of avionics manufactures are full of scary pictures of red and yellow mountain tops depicted on the PFD.  That or a low pass over a big cell tower.  Presented thus, it’s easy to see synthetic vision (SV) as solely a tool to avoid hitting things.  Yet even if you fly in the flatlands, SV is one heck of a cool feature to have.  Here’s why.

Let’s start with a tour of some recent avionics innovations.  When the first IFR GPS units were certified I remember flying an approach and thinking “This is great- every approach can now be flown like a Localizer approach.”  Flash forward a few years to WAAS- now every approach can be flown like an ILS, even better!  Well- what’s even easier than an ILS? A visual, of course, and SV had moved the state of the art to where every approach can encompass the same instant situation awareness experienced on a visual.  Of course, the published procedure must still be followed, but seeing the runway symbol and instantaneous flight path marker (FPM) crisply drawn on the PFD means the same intuitive techniques used to line up with a runway on a clear VMC day can be used when it’s 200-and-a-half.

For example, imagine a descent is being made to MDA on a non-precision approach.  No vertical guidance is provided, so the pilot has no choice but to dive to MDA, right? Not with SV- by controlling rate of descent so that the runway symbol stays at the minus 3° pitch point of the PFD, the plane is descending as smoothly on a 3° path as if on a glideslope.

Caption: Runway at three degrees and flight path marker on runway= stable approach

Another time SV can be a great aid to stabilized approaches is when cleared for a visual approach to an unfamiliar airport from a base leg entry.  These can be difficult to plan correctly, as the visual cues are difficult to interpret at a ninety degree angle to the runway.  Often pilots will turn final and find themselves quite a bit higher than anticipated.

If the runway has an approach with vertical guidance published, rolling out right on glidepath is child’s play.  By loading the approach and activating the leg to the runway threshold, the pathway boxes will be visible in profile.  They will be descending to the runway on roughly a 3° angle, so steering the FPM so that it lies over any pathway box will ensure the aircraft is descending so as to perfectly intercept the final on glidepath.



Caption: “Gunsighting” pathway box with FPM to ensure rolling out on glidepath