Haven't posted for a while but have just caught up on all the posts after a few days away. I'm no scientist but from what has been brought up in the technical posts......
The 744 had a gross weight calculation system as an option. This was years ago. We never used it, can't remember why. If Boeing built it back in the 80's, then a previous poster was probably right in assuming that the commercial departments of the world discounted the usefulness of such a system in favour of the lucrative "standard weights". Maybe it should be re-introduced. Just how much water are we carrying for those First Class showers.....?
Using a flex temp at a light weight or TOGA thrust at a heavy weight, in the same aeroplane, on the same runway, with the same environmental conditions, will result in you using roughly the same amount of runway. That's the whole premise behind using reduced thrust. You use all the runway and less thrust to get you to the required speed when you are light. If you are heavier, you need more thrust to get you to the required speed before you run out of tarmac. It follows that you should rotate near the same part of the runway regardless of your weight. This is great if you fly on and off that particular runway often. Not so great if you visit 100 destinations a year.
The trend vector shows on your air speed indicator, and is thus an indication of your rate of change of AIR speed (which is what you need to get airborne). The reactive windshear system uses airspeed fluctuations (among other inputs), that you see on the trend vector, to warn you when you get into a windshear situation. Before trend vectors previous posters used timed airspeed checks or distance to go markers (both of which gave you an idea of your rate of acceleration in airspeed). If you have a trend vector, you don't need a timed check or distance to go markers (although Bitchin' Betty the RAAS lady will calmly tell you that you have 1000 remaining). The trend vector is more or less instantaneous and is thus more accurate than a timed check, or gut feeling as you whiz past the distance to go markers.
If we have
- GPS
- Trend Vector
- Wind Vector
- Runway length
- Weight (an accurate one)
- Elevation
- Temperature
- Runway conditions
We should have all we need to tell us whether out acceleration/energy is sufficient to get us airborne before the end of the runway. I know this is all stuff that we work out before we blast off, and that the speeds we come up with are supposed to cover us, but humour me and read on.....
The first three items in the list are aircraft system derived.
The remaining ones are what we punch into the FOVE/BLT.
If you can combine all these elements, (plus a few more, including Bitchin' Betty) would you not have a system that could tell you instantaneously (as the reactive windshear system does) that you have insufficient energy to get off that runway on that day?
It could activate when TO thrust was set (Flex, Assumed Temp, or TOGA) and give you the option of going TOGA straight away or discontinuing the takeoff.
This all makes perfect sense to me at the moment, but feel fee to fire away as I'm sure there is something I haven't considered that will see my brilliant idea shot down in flames!
