AN/ASN-92 INS Part IV: Fix Update and Troubleshooting

Parenthesis: INS, vC and Positional Imprecision – A Chat with F-14 Radar Intercept Officers

In my long quest of understanding the F-14 and its avionics, I stumbled upon the imprecisions caused by Carrier Operations (see Part III of this series). It is indeed one of the very first things a virtual RIO notices when operating from a Carrier the first times. I was almost shocked by the magnitude of the difference between the actual heading indication provided by displays and the “real” heading.
A spontaneous question soon arises: “how did the crew deal with this problem in real life?”
No one can answer this question better than former F-14 RIOs!

I had another conversation with Dave “Bio” Baranek. He flew the Tomcat in the glorious early days, having joined the Navy in 1979. In his book, Tomcat RIO, he talks about a TARPS mission. A picture (right after page 102) represents a flight plan, something along a PPL dead reckoning-based log, to give you an idea. However, if the INS was so imprecise, how could they thoroughly follow the scheduled plan?

Although “state of the art” when designed, the [Tomcat’s navigation systems] seemed out of date and barely adequate just a few years later. But to get right to the point: in my experience it wasn’t as bad […] Most of my F-14 flying was pre-GPS. But in my recollection, heading info was accurate unless you had a system failure — which was rare.
[…] As we flew ahead of the carrier after launch, the pilot pushed the HDG Pushbutton and that made everything line up. This was routine. In fact, forgetting to do this was the basis for a brief episode in Tomcat RIO:

(The situation was my pilot Hooter and I were discussing a navigation error during a flight)

“I forgot to synch the compass,” he said. Pilots usually did that right after takeoff as they flew away from the enormous metal mass of the carrier. Don’t ask me to explain magnetic fields and their effect on our swing-wing jet fighter’s compass, I just know that when Hooter pushed the Synch button our displays shifted by 20 degrees. We were 60 miles south of our station! The INS was fine, as things turned out.

(In the end, this instance and another led us to realize we’d become complacent.)

But that was the only time in my 2,500 hours flying Tomcats that I had this problem. Of course, it wasn’t an issue when we started up ashore. On the other hand, the INS could drift or outright fail, and I mention that several times in the book, but I actually mention the possibility of it failing, and how we took steps to be prepared for that. It didn’t actually fail that often.

In any case, heading on the BDHI was accurate to one degree unless we had a real problem […].

Dave “Bio” Baranek – F-14 RIO

I also had a chat with Scott “Weird” Altorfer, Radar Intercept Officer in the VF-154 and VF-201, from 1993 to 1998. Being a RIO in the “post-GPS era” changed many things, and provided an incredible tool to improve and simplify navigation.
In fact, it looks like I overestimated the problem!

[…] in the real world, we simply did not care that much about the levels of precision you describe, probably because everything pretty much worked most of the time, and if it didn’t, we had a wingman and a GPS.

[…] If my INS dumped mid flight, I’d break out my little book of tests, run them on the way home, and write a gripe in maintenance control.
If my compass was off up to 10 degrees, I might not even notice! Radio navaids meant a needle points to them; landmarks on the ground don’t move, and the boat was always steaming around, anyway, so finding her was both an art and a science.

[…] For my TARPS missions over Iraq, I had my route programmed into both the Garmin and the INS. If they agreed, great, if not, I’d use the GPS.

Scott “Weird” Altorfer – F-14A RIO

Both comments are fascinating. From one hand, we can assess the revolutionary impact the Global Positioning System had in the military, before it landed in our daily lives. They are also witness of the ingenuity of people that found a way to improve their life by means of a simple commercial device.
On the other, they are a testament to the technical quality of a device developed more than 60 years ago that, failures aside, was capable of precisely guide a fighter jet to their objectives.

Translating this into DCS is not immediate: different players look for different gaming experiences, some issues are not existing (random failures can be activated, but they are arguably enjoyable). Nevertheless, these conversations give us a couple of ideas for more realistic ops:

• the usage of the GPS (NS 430). Often dismissed and probably not worth the full price if purchased only for the F-14 (unless a 3D model is introduced), it is definitely a nice addition in a post ’90s mission. It enables more complex and precise flight plans and map-scale navigation;
• the AN/ASN-92. As discussed in the previous chapter, the re-sync of the AHRS happens automatically, but it is a factor to be aware of, and worthy of being part of everyone’s SOP. Although the question about the functionality of the HDG Pushbutton in DCS remains (I have raised it with the devs already), the Radar Intercept Officer, even the Casual player, should be aware of this problem and work with his pilot to solve it when operating from a Carrier.