Digital Nerd

Thursday, August 25, 2005

Mother Nature - from Boeing

Boeing blog:

Michael Patnoe


When we talk about flight testing an aircraft as technologically advanced as the 777-200LR, people often forget how many airplane performance requirements are tied to something as common as the weather. So my work as meteorologist helps determine what we can do on any given day, and where.

Meteorologists offer weather support for a variety of Boeing programs. We also do analysis for engineers designing equipment. When it comes to certifying a new airplane, our basic job is to help the flight test crews find the weather conditions they need to complete the tests.

For example, I do a lot of "icing" work. Icing is defining how much ice an airplane might pick up on an extended twin operations (ETOPS) diversion. These are twin-engine flights over the oceans. One concern is what happens at a cruising altitude of around 30,000 feet if the airplane loses an engine and cabin pressurization. The pilot would need to drop down to 10,000 feet, where icing can be a big issue. Certifying an airplane for flight in ETOPS means demonstrating it can handle whatever amount of icing it might pick up in a diversion to an alternate airport.

777-200LR photo

Flight testing through the winds and clouds last month.

Then there are the winds, tailwinds, headwinds and especially crosswinds. It's difficult to find the crosswinds we need to certify because airport runways are designed to avoid them. We help them find the right regions to look at and suggest airports they can use the next day. One airport in Iceland is very good but expensive to get to. It has runways that cross each other, so almost any direction the wind is blowing in you can get a crosswind. And it's blowing there all the time.

In looking for crosswinds, we also check for weather systems - where the cold fronts and warm fronts are going to be. That's usually where the wind is going to be. Different locations have their own effects that influence how strong or weak winds might be. Once we select a few airports, then we look more closely and predict when the winds will peak.

Typically in Flight Test we have a window of time to find something. Initially we try to find the required conditions as close as possible to Boeing Field in Seattle. We look in the western United States and expand from there as we begin running out of time to find the conditions we need. We have many tools at our disposal, such as a weather data service and access to weather computer models.

The only remote testing where I go with the airplane is when we do community noise tests. We usually do these in Glasgow, Montana. Noise testing for certification needs to be done in a very narrow range of atmospheric conditions. The atmosphere absorbs different levels of sound, depending on temperature and relative humidity. It's actually a very complicated relationship. There also is wind, which can blow sound away.

My job is to try to predict the best time for testing. It's one of the more stressful jobs we do as meteorologists because there's a big crew of people and sometimes the optimum time might be at 2 a.m. If the test crew shows up at 2 a.m. and the conditions have changed and we can't test after all, the crew isn't very happy. But, our Flight Test crews are pretty supportive of meteorologists. They know predicting weather is not an exact science.


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