After reading this post after writing it, it has turned into a bit of a biology and basic radio navigation theory post. But this is pretty much necessary to understand the training and operation of aircraft for instrument flying. The short version for those that don't want to read into it, instrument flying is tiring and hard work but rewarding when it all goes well and solo navigation exercises are awesome and great fun.
Instrument Flight Training
In the commercial aviation world all flights are operated under what is called instrument flight rules (IFR). These are basically a set of rules that allow everyone to safely fly around and navigate with no external visual references and are used regardless of whether the aircraft is in low visibility conditions or not. As these are the set of rules I'll end up flying under, the training for them starts fairly early on in the programme.
As Arizona isn't known for its instrument weather conditions, and because we're actually operating the flight under visual flight rules (VFR), instrument flight is simulated using a device known as a hood. This is basically a piece of plastic like a very large peaked golfers cap that prevents you from seeing outside when wearing it but still allows you full view of your instruments. The instructor will then act as a look out for navigation and traffic avoidance purposes and anyone in the back seat can also help with this if there is someone there.
First a quick lesson in aviation physiology, bear with me here it's kind of necessary to explain this in order to understand the difficulties that can be experienced with instrument flying. Instrument flying is an odd experience, you have to learn to ignore all the signals your body is given you (known colloquially as 'seat of the pants' flying) and it's very easy for your body to confuse the type of acceleration acting on it. A lot of the acceleration information is through the movement of fluid in the inner ear, specifically something known as the vestibular apparatus. There are 3 semi-circular canals which measure angular acceleration and two lumps of calcuim carbonate which measure linear acceleration known as otoliths all of which are covered in tiny hair-like structures. As the fluid of the inner ear moves past these hairs during an acceleration the brain the identifies which direction the acceleration is acting in.
Sounds simple so far... the problem is that the brain at an instinctive level is actually quite stupid and without external visual references to back up these acceleration feelings they are pretty much meaningless. An example of this with the otoliths that measure linear acceleration, when you accelerate in the horizontal plane you get the feeling that you are leaning backwards. Try this the next time you are in a car (I should probably add as a passenger and don't try this if you suffer from motion sickness, it won't end well!), close your eyes before the car accelerates and you'll feel like you are leaning backwards in the seat, the opposite is true in a deceleration. But why is this relevant to flying? Well, when you accelerate and get this pitch up feeling you naturally want to pitch down, but this will actually cause you to lose altitude. Even worse in a deceleration you instinctively want to pitch up which will further increase your angle of attack and take you closer to a stall. What you have to do is ignore these instincts and trust the attitude indicator and altimeter to ensure you remain at the correct altitude. It isn't just this level of flying that affected as well, pilots of carrier launched fighter jets take their hands off the controls and hold onto a couple of handles in the cockpit during a catapult launch. There are a couple of reasons for this, one is to prevent them from moving the throttle or control stick due to acceleration forces the other is to prevent them from pitching down into the ocean as they come off the end of the carrier because the acceleration force is so great it feels like there a massive pitch up moment that needs to be counteracted even though none exists.
It doesn't get any better with angular accelerations either, as stated earlier acceleration are detected by the fluid of the inner ear moving hair like structures in the semi-circular canals. In a constant rate turn there is no acceleration so the hairs all stand back up again, this leads to the sensation in a turn that you are actually flying straight and when you do level off it then feels like you are doing a turn in the opposite direction. This is a very weird feeling and it takes a lot of effort to override your brain and trust your instruments to ensure you don't inadvertently turn again. There is also an acceleration threshold for the inner ear to detect movement, if the acceleration rate is too low then a turn can start without you realising it and there are numerous cases out there of pilots who have got themselves into cloud and then lost control and crashed a lot of the time due to a slow turn rate sending them into a spiral dive. I was fortunate when at university to do a flight test course where we were demonstrated a spiral dive and told not to look outside, I was surprised when we started to pull out of the dive at about 60 degrees of roll and 50 degrees nose down pitch as I genuinely hadn't felt any movement up to that point. That one demonstration taught me that you always need to trust your instruments unless you have a valid reason not to.
So with that said, since we can't see outside during instrument conditions then how do we actually navigate around? At a simple level the answer is two things, NDBs and VORs. NDBs are Non-Directional Beacons and basically it's an antenna that sends out a signal in all directions to say where it is in the 190-1750kHz range, this signal can then be picked up on a receiver on the aircraft known as an Automatic Direction Finder (ADF) and to be honest the entire system is rubbish! The system was supposed to have phased out decades ago but for some reason hasn't been even though nobody really uses it since it's so error prone. But the licence skills tests still include NDB work so we have to learn how to use them. Initially the use of all radio beacons regardless of type is the same in that they need to be tuned and then identified. Tuning is as simple as looking at the station on the chart and tuning it in on relevant navigation uni, for the Chandler NDB this required tuning 407kHz. It is then identified by listening for its Morse code identifier, although Morse code is almost never used these days it's still alive and well in aviation. Usefully the Morse identifiers are also shown on the chart to help with identification. After it's identified the ADF needle then points to the magnetic bearing of the NDB and all navigation is based off this. There's no way to set a bearing for it to point to, but it's better than nothing though it is fairly inaccurate. It also doesn't tend to be coupled with Distance Measuring Equipment (DME) so although you know what bearing you're on you don't really have any real idea of how far you are from the station. When turning onto it and when close to it the error of the instrument can be as much as 10 degrees. So a more accurate system is usually used.
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| Extract from the Phoenix Sectional chart showing Chandler (CHD) NDB and Willie (IWA) VOR |
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| Old Style VOR Display |
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| VOR Display from G1000 system |
At this stage of instrument training we're just looking at the basics such as tracking in and out of a beacon on a specific radial (or bearing) and intercepting a specific bearing. As the training goes on more complex elements will be added to this as we properly start to navigate by sole reference to instruments.
Simulator Flying:
Something that has been introduced since my last post is simulator flying lessons. These lessons are primarily used for training instrument techniques in a safe environment where the action can be paused to cover a lesson point if required. To be honest whilst the sims are good and are great for learning navigation techniques from they are not great for learning to fly the aircraft as they just don't feel right. The throttle and mixture response it totally different in the simulator when compared to the aircraft and the rudder pedals might as well not be installed given how far removed they are from how they work in the actual aircraft.
One of the great things the simulator can do though is train you for procedures that it's just not safe to fully do in the actual aircraft. On one simulator session alone was I faced with scenarios involving a failed battery, an oil pressure decrease that led to an engine seizure (simulating an oil leak) which required an emergency landing. I also had an alternator failure which at one point led to a total loss of electrical power (interesting in an all electric aircraft!) and had to try and get emergency power back. Obviously these are things you can never actually practice in the aircraft but it's great to be able to properly run through the checklists and troubleshoot a problem and find a solution.
Solo Cross Country Flying:
Almost all my solos these days are cross country navigation exercises of about 2 hours in length usually covering about 200 nautical miles or so. These routes are great for building confidence and decision making skills. Navigation out here is fairly easy, the visibility is fantastic and all the mountains around make for really easy reference points. These flights do tend to be quite early in the day and it's not uncommon to be off the ground by 6am, which means needing to get in a some time between 4am - 4:30am to start preparing for the flight. Whilst it does lead to tiring days it is very rewarding and at least flying at that time of the morning it's still fairly cool, only in the high 20's! As these cross country routes progress it'll start leading to landings at different airfields and will eventually build up to the solo cross country qualifier, but that can be explained some other time.
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| Typical navigation route shown on the Phoenix Sectional Chart |
Well tomorrow, has 2 milestones. Firstly it's a SPIC flight which is Student Pilot in Command, this basically involves going up with another instructor for an instrument flight where they'll act like an air traffic control giving you vectors and altitudes to fly to see who the instrument work is coming along. All the handling of the aircraft is up to me as the student pilot however. Secondly tomorrow will also mark a total of 100 flying hours in aircraft since I took my first flight back in 2011 back when getting my PPL. To say I came out here with about 55 flying hours it's come around very quickly.
Later on this week I've got the first of the night flying exercises planned which according to people on previous courses are great fun so I'm really looking forward to those. Then all been well next week will be progress test 2 which seems to have come around very quickly indeed. This is the equivalent to the manoeuvres part of a PPL skills test so will be quite intense. After that (assuming I pass it) it'll be a lot more instrument work with a few solo navigation exercises thrown in as well.
