CPL day 5 part 2

Because the weather was rubbish for visual flying I was able to get a second flight in on Friday which was a bonus because it meant I was still in instrument flying mode and also provided some mitigation against the miserable start to the week.

Did some more general handling with climbs, descents and turns to polish the edges on that, followed by some limited panel work. Limited panel means that one or more of your instruments have failed and you have to infer the missing information from a combination of the remaining ones. Typically, and for the test, it will be the vacuum driven gyro instruments the AI and DI that have "failed". To simulate these failures, the instructor will stick a rubber suction cup over the instruments to obscure them.

Did some basic climbing and descending which isn't too bad since you still have a VSI, ASI and altimeter so you can set the correct speed for the climb/descent and level off at your desired altitude. However, since you have no DI to maintain a heading to and you can't really use the compass because of it's errors, you have to closely monitor the turn coordinator to ensure you keep the wings level and don't inadvertently enter a slight turn and lose your heading.

It really gets "fun" when you have to do turns. You keep your altitude in the usual way by monitoring the VSI and altimeter, but you only have the compass for heading. Because of the compass turning errors, the only realistic way you can perform turns is by doing a rate 1 turn (which is marked on the turn coordinator) so you have a known rate of turn and time it. So if you're turning from 090 onto 240 (150 degrees) at a rate of 3 degrees/sec (which 10 seconds foe every number on the the VOR ring which helps work out how many seconds to turn for) you'll need to turn for 50 seconds and try to maintain an accurate rate 1 turn all the way through. So you start your stopwatch, roll into the turn, maintain rate 1 and then as your desired time is reached you start to roll out of the turn. You then let the compass settle and if you've done it spot on, your new heading should be correct.

Of course it's all very much easier said than done.

Firstly what happens if you need to turn from 090 through a heading of say 107 degrees? You've got to be very quick at division and multiplication by three in your head which is not at all easy when you're struggling with flying correctly and instrument failure. The use of the VOR ring helps here - you can set your current heading at the top, count the number of whole digits which are between your current heading and the desired one (in this case 3 which equals 30 seconds). Then the remainder - do you add a fourth 10 seconds and subtract the difference (roughly 4 secs), or just add the remainder (roughly 6 secs). If you alternate between the two it's all to easy to add the remainder instead of subtracting it or vice versa (I did this a couple of times) which could quite easily result in an error of 20 or so degrees.

Then there's the turn coordinator. Do you position the needle/aircraft image wingtip directly on the needle, or so the point of the needle is at the bottom of the mark, or the top? It quite probably varies from aircraft type to aircraft type, and possibly between aircraft of the same type.

As far as my results go, it wasn't very successful and I was mostly 10-30 degrees out. Dick pointed out the quirks of where to position the turn coordinator needle after we'd had a few poor attempts. On the PA-28 (G-BXLY) you need to position the needle on the bottom border of the rate 1 turn mark; I'd been trying to keep it in the middle of the mark. It may not seem like much, but an under turn of only 0.25 deg/sec over 50 secs would result in an error of 12.5 degrees which is quite significant. But Dick was happy with my technique.

A similar return on instruments for a visual approach went well and the landing was pretty reasonable with only a slight balloon on the flare.