PVI. The para Visual Indicator. Gives the CM1 (PF on LWMO ops) an indication of the runway centreline on low vis take offs. The information comes from the ILS LOC.
Called a PVD (Para Visual Dispaly) on Boeings - just to be different!
You two are right, of course. But it was not a user-friendly device, and only gave us a slight reduction in the RVR required. It was only in your peripheral vision, because you were still watching the rwy centreline lights (of which only one or two are visible at a time in low-vis, but you have to use them). As the PVI (LCD display) was only at arm's length, it was out of focus, particularly for those of us with presbyopia.
[For those not au-fait, the most difficult stage of a low-vis take-off is the beginning. Once the centreline lights start to "stream" under the nose, the fact that only one or two are visible at any one moment ceases to be a problem.]
There was a similar idea to the PVI on the A310, but I found it much easier to use because it was in the form of a head-up display, focused at infinity I think.
It's a better device than the Boeing one which looks like a horizontal barber's pole. It rotates if off the centrline, but it's not that obvious which way you have to turn to get back on!
I am with Dan here a bit. PVDs had a very dubious history when the were first introduced in the mid 60s. Then they were used in pitch and roll not just yaw. The issue of course is whether they are telling you to follow them or oppose them. With two or perhaps three as they were first deployed this clearly confused a lot of us when we tried them.
I can also understand how this might not be a problem with one in yaw as TopBunk suggests.
Indeed I remember a similar issue with the Harrier rudder pedal shakers - only one shook and was that the one you had to push or leave alone? We sorted that out with the 'stamp out vibration' motto.
I understood the idea was to be consistent with the 'natural' view out of the window - if the outside world moves to the left, you need left rudder to bring it back again (similar sense for other axes, but by the time I got to the Trident, only the lateral mode - for take-off and roll-out guidance - remained). So one had to think of the little diamonds as belonging outside.... but whatever worked for the individual was OK.
And how about the old cylindrical Directional Gyros, not exactly intuitive until one got the 'roll the numbers down the slope' mantra off pat. And while we're at it, which way should moving tapes move? High numbers at the top, so the tape slides down as the quantity increases, or vice versa? Good cases can be, and have been, made for both. And finally don't let us forget that the some Russians use horizons that are the wrong way round, the little airplane moves while the horizon remains steady relative to the aircraft, help!
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