Just to pick up on Chug's point. I have spoken with serving Nimrod crew tonight and concern is being expressed by the fact that many of the really tough issues unearthed by the Nimrod BoI have merely been booted into the long grass. The crew I talked with are still very concerned about the airworthiness of this aircraft. In particular the use of Tank 7.
The argument for bringing Tank 7 back into use and the way it will be used has been far from convincing.
What has actually been achieved here? Missions continue. Problems concerned with not being able to use SCP continue. The BoI was far from definite about the source of the fuel leak, and the single wall pipework is still there.
The one thing that was clear from my conversations was the complete absence of leadership in the RAF, but an awful lot of arrse covering.
Here is a link to how Airbus have approached Tank Safety in in order to comply with JAR directives.
http://www.content.airbusworld.com/S...33igintion.pdf
Unlike Dreamliner, A380 is not using Inerting equipment but has gone for even more built in design safety.
"Airbus will demonstrate that the ignition source prevention features are sufficient, in and of themselves, to meet the aircraft safety objectives considering a permanent flammable fuel tank environment," EASA declares. "Airbus will further demonstrate through its flammability assessment that it has further upgraded its safety level by implementing design features, which minimize heat transfers to the fuel tanks, avoiding unnecessary increases in the fuel tank flammability."
There is no center wing tank on the A380, although one could be fitted on subsequent models of the aircraft (e.g., the 800-passenger version). Moreover, the air conditioning packs on the A380 are located on the forward side of the front wing spars, with insulation. Thus located, they are not directly under any fuel tanks, which is the case on the B747 and the B737; these models have experienced three fuel tank explosions in recent years - TWA 800 involving a B747, a Philippine Air Lines (PAL) B737 at Manila, and a Thai International Airways (THA) B737 at Bangkok. All three sustained explosions of the center wing tanks.
"The A380 air conditioning packs are in the 'shoulder' of the wing," the NTSB official conceded, but on a hot day on the ground, as was the case in the Philippine Air Lines and Thai Airways explosions, the airplanes didn't have the benefit of airflow to dissipate the heat of the packs, and this also would be the case with the A380 on a hot day.
The safety board registered its objections to EASA, which rebuffed the complaints. The Europeans seem bent on issuing special conditions for the A380 that focus on three sources of ignition, and the need to minimize them: electrical arcs, friction sparks resulting from mechanical contact of rotating equipment in the fuel tank, and hot surface ignition. "The applicant should perform a Safety Assessment of the fuel system showing that the presence of an ignition source within the fuel system is Extremely Improbable [that is, 1 x 10- 9, or one in a billion flight hours] and does not result from a single failure," the EASA said.
Airbus must account for a variety of fuel pump failure modes that can cause ignition (e.g., debris lodged inside pumps, poor bonding of components to structure, etc.). It's generally conceded that a pump immersed in fuel cannot cause ignition due to any failures. Indeed, that is why so many airworthiness directives (ADs) have been issued limiting the running of in-tank pumps to a certain minimum fuel level. This ensures that fuel levels in heated tanks (those with air conditioning packs located below) with flammable ullage would never drop to a level where fuel pumps would not be immersed - no matter what the aircraft's pitch, roll or yaw attitude. Yet, knowing this, Airbus apparently is not being required to locate fuel pumps outside the fuel tanks, where they would never be "not immersed" nor exposed to in-tank heated ullage. This logical avoidance step would also allow high voltage/high current pump wiring to remain outside of the tank.
Regarding specific FAA and NTSB objections to its special conditions, EASA was pretty clear in its view:
FAA: "Flammable conditions within the [Thai and Philippines jets] would have been reached in flight after these airplanes began to climb, even if the tank had not been heated."