The problem was the full tank as it relates to the weight of the aircraft. If your aircraft is very heavy, the engines don't have enough power to haul it up to a very high cruise altitude. The 767 is rather underpowered and you have to reduce your rate of climb as you go higher in order to maintain the necessary airspeed. For that reason it is essential that you don't load more fuel than you need (plus reserves) in order to keep your weight down. Keep in mind that a 767-300ER can easily fly Frankfurt-Brazil nonstop, so if you're just doing a short hop to one of the Mediterranean tourist destinations, you don't need more than a quarter of a tank full. This will allow you to climb faster and attain a higher cruise altitude. Otherwise, if you're flying long haul, you need to climb to a preliminary crusie altitude of, say, 28,000 and burn off some fuel before step climbing to higher altitudes as the aircraft gets lighter. Hope this helps.Misha

I have experienced quite a number of times these impossible drops in pressure. Once FL240 was 3,000 feet for me!Kitty MercuryCathay Pacific Virtual Pilot (CX252)