Sunday, September 7, 2008

Instrument flying in the GFPT

The Australian PPL syllabus requires student pilots to have completed two hours of instrument flying before attempting the GFPT test. Instrument flying is when the pilot flies the airplane only by reference to the instruments inside the plane, as opposed to visual flying, when the pilot looks outside the window at the ground, the sky and the horizon to find out where he is and which way is up.

The picture above shows the instrument panel of a Cessna 152 on the ground. Since the engine is not running, no suction is available from the engine-driven vacuum pump for spinning gyroscope-driven instruments such as the artificial horizon. This is why the artificial horizon shows the airplane as being banked to the left with a nose-down attitude, although it is sitting on even ground.

Luckily for us visual flyers, light aircrafts have quite a few windows. The big one at the front with bugs squashed onto it is the windscreen. That's the one you should be looking out of most of the time when doing visual flying.

Side windows are nearly as important, especially for clearing turns and checking where the airplane is in relation to the runway when coming in to land. Just try to fly a circuit in a flight simulator without changing views and you’ll realize how hard it is without side windows, especially when turning base or final.

The great thing with most Cessna airplanes is that they have a back window, which comes in handy for checking where the runway is after take-off and correcting for drift. And if you happen to fly a C152 Aerobat such as VH-IVW, there are even two narrow elongated sky windows for orientation when performing aerobatics manoeuvres.

Instrument flying assumes there is nothing useful to see through the windows. The airplane could be in clouds, or in conditions of poor visibility such as in heavy rain, fog or smoke. The way such situations are simulated in training flights is by having the student put on the so-called IFR hood.

The hood is like a big plastic baseball cap with a long curved visor sticking out the front. It is sometimes referred to as a view limiting device, which is as accurate a description as you can get since it prevents whoever is wearing it from seeing anything outside the cockpit, while still being able to look at all the instruments on the panel. In the purely hypothetical situation where the instructor would realise at 2000 feet and halfway to the training area that the hood was left behind at the club, a sheet of paper or a folded map stuck under a regular cap does a pretty fine job too.

Going back one step, why do we train for instrument flying in the PPL, since the holder of such as licence is only allowed to fly during daytime and then only according to Visual Flight Rules, i.e. with sufficient visibility to fly by reference to the outside, and never ever into clouds? Well, precisely because of what happens when one accidentally flies into clouds.

VFR flying into IMC conditions is one of the biggest killers of general aviation pilots. Research conducted at the University of Illinois in the early 90s showed that, on average, pilots start suffering from spatial disorientation on average 178 seconds after entering IMC conditions. That’s just 2 seconds short of 3 minutes. In each case, the (simulated) airplane entered a graveyard spiral with a predictable fatal outcome. The pilots being tested only knew they participated in an experiment about instrument flying, not that it was about spatial disorientation. There's a good CASA video on the topic here. Not very coincidentally, the length of the video is 178 seconds.

The rationale for instrument flying training in the PPL is therefore to teach VFR pilots how to get out of clouds as quickly as possible using only instruments. This is why the training concentrates on making turns, climbing and descending, and does not even mention about IFR procedures.

I really enjoyed these two hours of instrument flying. It is very challenging and rewarding at the same time.

The challenge comes from the fact that one has to keep a very quick scan going across the instruments on the panel. The eyes go from one instrument to the next, always going back to the artificial horizon between any two instruments. This is easier said than done. One problem I had was with not keeping a scan that was quick enough. I would then realise there was a problem once the problem had started to develop, making it harder to fix.

Or if the instructor gave me an instruction such as “turn right to a heading of 230 and climb to 2500ft”, my scan would concentrate on the Directional Gyro and the altimeter, and would forget the Airspeed Indicator. It happened once when the instructor attracted my attention to the ASI. The airspeed was bleeding, nearing the bottom of the green arc, approaching the stall. Not good.

One thing I noticed when flying on instruments is that I used the throttle a lot more than usual, making lots of adjustments to get the rate of climb where I wanted it. This was not good, since it introduced an extra independent variable into the system, i.e. one more reason why things may go wrong. The right way to do things was to set an attitude using the artifical horizon, see how the plane reacted, then adjust again when needed.

All in all I think I did good, and instrument flying really opened my eyes to a completely new way of flying the airplane, one where the relationship between power, attitude and performance becomes a lot more obvious. Thinking about it, the variables received as input and the ones available as output are the same for human pilots under the hood and for the autopilot. Not having to fight spatial disorientation may even make the job of the autopilot easier in comparison. But what makes it special for us humans is that we get such a tremendous amount of fun out of it.


Chris said...

Instrument flying is a good challenge, I always enjoy it when I get the chance. Have you got your GFPT yet?

I'm a GFPT pilot from central NSW and am getting close to finishing the Nav's.

Julien said...

Hi Chris,

Yes, I passed the GFPT test about 6 months ago. I really enjoy taking friends on local flights to the training area, but now I'm getting a bit bored with that and am really looking forward to passing the PPL test and discovering new places.

This post about Instrument Flying had been gathering dust as a draft for a long time. I needed a photo of an IFR hood to complete the post, and I only got around to taking it last week-end.

I'm finished with my PPL navs now, I have the PPL pre-test lined up for end of September, then the PPL test for end of October. Fingers crossed...


mark said...

Hi - i finished my pre gfpt BIF this week and the GFPT exam is up at Cessnock NSW - I did over 50 hours for it , mostly because the medical took so long to come through.PPL theory and NaVs November and December then hopefully out into the wide blue yonder!
I didnt wnat to get a gps before finished the ppl navs , but the Aussie dollar was falling so fast I releneted and got a Garmin 495 this week!