RNAV Approaches with a Portable GPS

As I mentioned in my other blog, last Fall I was forced to fly a RNAV (GPS) approach into Lynchburg with a portable GPS when the ceilings dropped faster than forecasted.  We managed ok but it was definitely a nail biter since my portable GPS is not approved for IFR approaches.

Since that time, I've been researching upgrading DKX for true IFR capabilities and I've concluded that the high cost of approved navigators is simply out of the question.  For example, the cost of a Garmin GTN 650 navigator is $11K US plus installation. When you add in the related other equipment--antennae, CDI, etc., the cost is well north of $17-18K Canadian.  That's nuts.  Almost 1/3 the cost of the airplane!

And considering that Garmin's Aera 660 Portable GPS (which is what I have) at $700 US contains many of the same features as the GTN650 , it's incredibly hard to justify the expense when you fly approaches so infrequently.

It certainly shows how TSO (Technical Service Order) requirements that the manufacturers must go through to certify their equipment really drives up the costs.

So until I upgrade for ADS-B next year, I'm going to stick to the status quo.

So having said all that, I've been looking how I can optimize the use of my portable GPS.  Technically, a non-certified GPS cannot be used for primary navigation on an IFR flight plan.  As I've mentioned before, DKX is legal for IFR but my equipment is in the same league as "stone knives and bearskins", to quote Mr. Spock.  So while I should legally be filing and flying the airways (using VOR's), no one does that anymore.  I mean no one.  Everybody goes "Direct" and ATC expects that virtually everyone can do that.  The only way that's possible is with RNAV equipment (which is short for Area Navigation) and that means GPS 99% of the time.  (Inertial Navigation is another, but that's limited to commercial jets).

So the fact that I'm using a portable GPS for enroute navigation, i.e., going direct, is not really kosher, but it's ok in my mind because a) I'm always in a radar environment so if you somehow got off course, ATC will notice and call you, b) I have Foreflight running as a GPS backup and c) the portable aviation GPS navigators are incredibly reliable.  I've had 4 or 5 over the years and never had a malfunction.  And even if one blew up in the air, I can always revert back to flying the airways using my NAV/COM radio and VOR's.

Approaches, of course, are a different story.  Nowadays, most GPS are WAAS (Wide Area Augmented System) capable and their accuracy is phenomenal.  And as you get closer to the ground, that accuracy is important.  My portable is WAAS capable too, but it doesn't really make a big difference since it won't let you navigate a profile below 1500 ft or so.  It has a cutoff feature that prevents idiots, like me, from using it for vertical guidance as you get close to the ground.

So how to fly an approach, albeit quasi illegally, but in a quasi emergency, using a portable?  Here's how to do it.

First, you must have a digital autopilot (like a TruTrak Vizion) coupled to the GPS.  Trying to hand fly the airplane while you force fit a portable to fly an approach is a recipe for disaster.  The workload is just too high.

Second, you must have personal minimums.  In the majority of cases, the ceiling can't be below 1000 feet, so the field is legally VFR (and the manoever is essentially cloud breaking).  That way, if your busted by Transport Canada or the FAA, you could argue that you were VFR the whole time.  Yes, illegally flying an IFR approach but not really compromising safety.

If legality is not an issue for you, and you're pretty confident in your ability, I would descend to circling minimums.  That way you can still manouever in the vicinity of the airport if something goes south at the last minute.

In a real emergency, I would fly right down to the LNAV mins.  I've done this many times practicing at my home field and it's perfectly safe.  Let me explain.

The Garmin 660 (and the other Aera series portables) come loaded with instrument approaches for every airport in North America.  Amazing.  Now, they are there for "monitoring" purposes only, and are not to be used to fly an IFR approach as primary navigation.  Never.  Not ever.  Ever.

To ensure that idiots, like me, are not tempted to do so, only the approach segment from the Final Approach Fix (FAF) to the Missed Approach Point (MAP) are included.  If you load and activate an approach, the GPS immediately provides course guidance direct to the FAF (and if coupled to the autopilot, the plane immediately turns towards the fix which is not helpful.)

The obvious solution, is to augment the approach with the missing waypoints, i.e., the IF (Intermediate Fix) and the IAF (the Initial Approach Fix).  Amazingly, these too are included in the GPS database (although not part of the approach...yet).

By retrieving the needed waypoints from the database, you avoid the big no-no of creating your own user defined waypoints and screwing things up.  It was this specific issue (creating your own waypoints) that made everyone very nervous when GPS's first came out.  And rightly so.  Real idiots (worse than me), created their own approaches from scratch and occasionaly flew into solid objects when the waypoint was in the wrong place.  Very poor form.

So the technique is a follows.  Note that the autopilot flys the plane the whole time.  No hand flying at all.

While enroute, and when you know what approach to expect, append the missing waypoints to the flight plan.  But make sure the plane keeps flying to the destination, until your cleared for the approach.

Once cleared, and directed to the IAF, go direct to the IAF using the autopilot.  While enroute, activate the approach BUT you must do this when the autopilot is in Heading mode (and not GPS NAV mode), or else the plane will prematurely turn to the FAF.  Once the approach is activated, redirect the plane to the IAF and reengage the GPS NAV mode.

Voila!  The plane will fly the full approach, sequencing throught the waypoints just like a certified unit.  You fly the profile using the Vertical Speed and the Altitude Select knob.

Once final point.  If you need to make a 90 degree turn at the IF (like most RNAV "T" configurations) you can't let the autopilot do this directly.  Without GPSS steering, i.e., turn anticipation (which the certified units have), the plane will overfly the waypoint before it turns to intercept the next leg, usually at a 45 degree angle.  This maybe ok enroute but doesn't work on an approach.

The solution is to briefly put the autopilot in Heading mode, anticipate the turn by 30 sec or so (remember a rate one turn is 3 degrees per sec, so 30 sec for a 90 degree turn) and use the heading bug to turn the plane.  As it approaches the final approach course, re-engage the GPS NAV mode and the autopilot will quickly recapture the inbound course and fly the plane right to the runway.

Piece of cake.  Fly safe.