Week 45: Instrument flight

Flying this week has completely changed, from now on views out the window for 90% of the flight are purely for enjoyment rather than reference. The visual flight rules phrase for all intents and purposes has now finished (asides from a few upset recovery flights), further details flown with reference to the array of screens, dials, and instruments within the cockpit. Given this is the type of flying that will dominate our careers, the flights have almost taken on a different feeling, with a lot more procedural flying giving the perception of a more professional cockpit environment. That's not to say we were zooming about yelling yee-haa at the top of our lungs, but instrument flight inevitably leads to a very different mindset. 

Holding was the first port of call, initially looking at VOR (VHF Omnidirectional range) and NDB (Non-directional beacon) holds. These two things are ground based navigation facilities, sending out horizontal signals that aircraft can utilise to orientate themselves, as well as navigate from/to. They are also often used as a fix for holding, and as Hamilton has both types there are holds/approaches established over each, which were used during my simulator sessions. For those that care, an NDB is pretty much just a vertical aerial, and that's a VOR ----->

Given how intelligent modern aircraft are, holds tend to be flown with the autopilot engaged, the flight management computer continuously updating the aircraft's position in space so that the ideal hold can be flown with varying angles of bank. As good as the Garmin is, it's not that good so hold flying is as much about mental calculation as it is accurate flying. The calculations are focused on two areas:-

1. Timing- the ideal scenario is that the wings level legs are flown to last 60 seconds in still air conditions, the corresponding distance giving the hold a fairly standard size. Nil wind is incredibly rare, so during the outbound leg if there is a headwind one additional second is added per knot of headwind, whereas with a tailwind one second is subtracted per knot. Therefore a comparison needs to be made between the aircraft's true airspeed and ground-speed, and how that affects the times, the resultant difference applied accordingly.
2. Tracking- If there is a wind blowing across the hold, dependent on which side it's coming from one of the turns will be made a lot tighter and the other significantly wider. Without some sort of adjustment this is an unacceptable situation, as the aircraft will quickly leave the protected holding area and tracking back to the holding facility becomes increasingly more difficult. At CTC the double/triple drift technique is used, and as a result the outbound/inbound legs are not parallel but the hold is significantly more manageable. I've attempted to show the holds pictorially (sorry it's naf!); with a wind from the holding side the drift is tripled, and with the wind on the non-holding side the drift is doubled. This means that with the tighter/wider turns the new tracks help to achieve the correct inbound track. Both holds start at the cross, and go clockwise. 

Once the holds were meeting the right standards, procedural approaches were flown commencing from the hold facility. This involves flying away from the hold descending to a certain altitude, turning back onto a track towards the airfield, then descending at a certain rate of descent to achieve a procedure designed descent gradient, a gradient which ensure separation from obstacles on the approach. In some cases these approaches contain level advisories whereby the aircraft should be at a certain altitude at precise distances, but if the airfield has no facility for transmitting distance information the planned rate of decent needs to be flown as accurately as possible. These procedures create a much higher cockpit workload than with a visual approach, and to ensure a good approach is flown core skills of pre-planning, briefing and prioritisation are vital. The chart on the left (or plate) is for the VOR DME approach to runway 15 at Laos. The top section with a river running through the centre is a top down view which aids lateral planning, and the bottom section gives guidance for the vertical profile (The race-track hold can be seen to the right of the magenta text). There is a vast amount of information contained on the plate, a lot of which needs to be taken in prior to the approach being flown. This demonstrates how the workload quickly ramps up, as there are many criteria that must be met for the approach to be deemed safe. Plate not to be used for navigation.

Next up is GPS approaches, where imaginary points in space establish waypoints, but in essence the aircraft is flown as if there was something on the ground. The Garmin system is going to be of vital importance for this element, and without sounding like an idiot I am more scared of tuning the system than I am of flying the aircraft! We'll then move onto precision approaches using the instrument landing system, which ill talk about more next week.