As I don’t fly pressurised aircraft (yet), I spent most of my flying time at altitudes between mean sea level and 10′000 feet. I never flew below mean seal level (a trip to the Netherlands would make it possible), but I popped above the 10′000 feet limit occasionally when flying over the Alps.

The airspace at and below 10′000 feet is like my flying home. It’s not always an easy place to fly, but I like it. Most of the icing is there, as air-temperature above is too cold for that. Thermal and orographic (caused by wind over mountains) turbulence occurs below 10′000 feet.

The view from there is much better as from FL300 (sorry jet guys), and there is much less traffic there than where the airliners, business jets and turboprop do fly. And descent planning is much easier when there is only 3′000 feet to loose to the IAF.

When I read that “sustained flight below 10′000 feet is not recommended“, I did not like that – particularly as it was part of Boeing check-list. If it is not recommended for airliners to fly below 10′000 feet, what about light aircraft then ? Shall I always request Flight Level 110 ? Shall I buy an oxygen bottle and cannulas ?

Well, let’s have a closer look. It all started with a an aircraft which flew for 10 hours with a cracked windshield. The cracks were small, the windshield shown no deformation, this incident was a non-event. In the forum discussions on this incident, the procedures to apply in case of cracked windshield for various type of aircraft were exposed.

Most of these procedure include a descend, aiming at reducing the pressure difference between the cabin and the outside air. If the windshield is seriously damaged, the pressurization could break it, leading to more serious trouble. Most Airbus checklist require a initial descent to 23′000 feet, and lower if required.

As often, the Boeing procedure is less… academic, and probably easier to follow: descend to 10′000 feet or the minimal safe altitude, whichever is higher. Here comes the note at the origin of this post, extracted from a Boeing 777 abnormal checklist: “Sustained flight below 10,000 feet is not recommended due to greater risk of bird strike”.

So what ? Not only my favorite place has most of icing, extra turbulence, and moreover we have most of the birds ? Even if Boeing thinks that sustained flight below 10′000 feet is not recommended, I like to do it, and I’ll continue !