So is it easier to handle the plane in a headwind, tail wind or crosswind. Which is preferable for take off and which for landing - or no difference?
When an aircraft is sitting on the ground, with a headwind, that's airspeed that it already has. It doesn't need to be accelerated to the same degree to reach lift off speed, so a headwind will make the takeoff roll shorter. A tail wind has the opposite effect.
Landing, a headwind reduces the ground speed, and so means the aircraft has less energy (relative to the ground) to get rid of, so less heat in brakes, and shorter landing roll. Landing, the tailwind adds to the groundspeed, and means we'll need more runway.
The manufacturers place limits on the acceptable wind, and tail winds generally cannot be accepted above 15 knots, and may be restrictive above 10.
Crosswinds. During take off they try to push you off the runway, so you'll sometimes need quite large control inputs to keep the aircraft straight. Those inputs will generate drag, and will reduce the takeoff performance, though not dramatically. At rotate you need to be very careful, as you lose the control that having some wheels on the ground gives. Generally, though, not a big deal.
Landing is a bit different. You will have seen the aircraft tracking towards a runway, appearing to 'crab' sideways. That's not quite what they are doing. We turn into the wind, to that the resulting drift gives us a track down the runway. Every time there is the slightest change in the wind, we have to turn to both fix the effect that the change will have had (i.e. it will always have moved us in one direction or the other before we can correct for the change), plus we have to then reestablish that correct track. At the crosswind limit, that drift will be in the order 15º.
At the bottom of the approach, we have to flare the aircraft. Once you've completed that, you need to use rudder to align the aircraft with the runway. That rudder input has to be done smoothly, as a secondary effect of any rudder input is roll, and you don't want any roll near the ground, and in particular, you don't want any towards the downwind side (and that's the effect that the straightening rudder will have). Of course, as soon as you even start to straighten the aircraft up, you're cancelling out your wind correction, and the wind will start to take you towards the downwind side of the runway. In smaller aircraft, that can corrected by a little bank in the opposite direction, but it's not really an option on the big quads, as engine clearance will become an issue (i.e. an engine scrape). On the Boeings, you can actually land with all of the drift still intact, and whilst a tad uncomfortable at the back of the aircraft, it is a very viable technique. AB are limited to 5º of drift at touchdown.
Even once down, the wind is still trying to push you to the side of the runway, so you may have to use quite large and abrupt control inputs to ensure the aircraft stays where you want it.
Geometry comes into play here too. These aircraft are very large, you have to allow for the fact that the gear will be appreciably on the downwind side from the coughpit. If the pilot places himself on the centreline, as you would normally, and you have 15º of drift, the main gear will be displaced about 25 feet to the side for every 100 feet of coughpit/main gear separation. To alleviate that, you need to move yourself upwind by an equivalent amount, to ensure the gear stays near the centreline.
And all of this becomes much more interesting in the wet....
Anyway, headwind is generally best. Light tailwinds aren't an issue, but they become limiting very quickly, and crosswinds can be very hard work.
Also in the discussion about fuel loads, what's the minimum fuel load you would land with say after MEL_LAX? Mr Julesmac goes off his brain if I let my petrol get to the "lights on" stage because of the cough in the bottom of the tank. Is that an issue?
The final fuel that we land with is affected by many factors, some of which apply to earlier phases of the flight and become irrelevant at the end. LA is a case in point, as the aircraft generally have extra fuel loaded to cover the depressurisation 'contingency', and as that will almost always still be intact, it has the effect of increasing the arrival fuel.
In percentage terms though, the cars that I've owned mostly have the low fuel light come on with about 10-15% fuel remaining. The A380 has fuel capacity of roughly 250 tonnes, and most landings would occur with about 12 tonnes remaining....about 5%. The absolute lowest that we could legally land with would be in the order of half that, so about 2.5%. Most of the fuel tanks are run dry during the flight...so I guess Mr Julesmac would be having a heart attack.
And when you read of planes having to dump fuel before an emergency landing, what if it's urgent you get down quickly as opposed to having time to burn fuel?
All aircraft have a series of limits laid down by the maker. For the A380, it has a maximum take off weight of 569 tonnes, and a maximum landing weight of 391 tonnes. It burns fuel at an average of about 13 tonnes an hour, so, if burning was the only way of getting rid of the weight, you'd be committed to a 13+ hour flight, just to reach landing weight (assuming you took off at the max, as we did yesterday, on the way to Dubai). Dumping the fuel that you can dump (not all if it can be in the AB, though the Boeings can) will take about an hour. You can land at weights above the max, but the sink rate becomes very critical..it must be smooth. Landing at a lower weight will reduce the approach speeds, so you'll have a lot less energy to dissipate after touchdown, and runway length will be less of an issue...plus the tyres are more likely to remain intact.
If you are in a desperate hurry to land, then you'll just do so, and not worry about any limits. The condition of the aircraft afterwards will not be a consideration. But, the vast majority of aircraft incidents are best handled by hastening slowly. Working methodically through what needs to be done is much more likely to give a happy outcome than rushing into any particular solution.
