Speed of sound in knots Patch#

They have the same airspeed, but different groundspeeds. The 777 is facing a jetstream going at about 100 knots, and the MD-11 is being pushed by it.

Speed of sound in knots Patch#

The label tells us that it’s at Flight Level 350, or 35,000 feet, and going at 550 knots over the ground (well, over the sea, but you get the point.) At the bottom, an Etihad flight - a Boeing 777 freighter bound to Miami from Zaragoza, Spain at 34,000 feet - is doing only 457 knots despite having similar speed capabilities and being in pretty much the same patch of sky as the other plane. At the top in the image below is an MD-11 tri-jet flying from Philadelphia to Cologne, Germany. But in airspeed, you’re still quite subsonic.Ī tale of two cargo flights seen over the Atlantic on Wednesday helps understand the concept. You’ll get to London faster, sure, because you’re moving faster over the ground. So, you may be flying over the ground at 800 mph, but within the jetstream, the plane’s airspeed is still Mach 0.85. That’s the wind that blows west to east at high altitudes, and can make eastbound flights much faster than in the opposite direction. So when the otherwise tame jetliner taking you to London is doing a blistering 800 mph, it means that, just like a boat in a river’s current, it has hitched a ride in a fast-moving stratospheric jetstream. That’s the number that counts when going supersonic, for example. So the speed that really matters to pilots is known as airspeed, or how fast the plane is moving relative to the air around it. But planes are surrounded by moving air, and they fly inside of it. When we see reports of a plane reaching over 800 mph or other similarly humongous speeds, well above the usual speeds around 550 mph, that’s the aircraft’s groundspeed.

It’s happened before, but this week a Virgin Atlantic flight was clocked over 800: precisely at 801 mph, over Pennsylvania. Until the Mach 2 Concorde entered service in the mid-1970s, that was the only documented example of a plane intended for passenger service exceeding Mach 1, or the speed of sound, which is about 760 mph at sea level.īut lately, social media has been lighting up with excited reports that Boeing 787s have been pushing close to 800 mph. The crew nosed the plane over, and in a controlled dive through 41,000 feet, the four-engine jet broke the sound barrier, reaching a speed of Mach 1.012. In August 1961, a newly-built Douglas DC-8-43 passenger airliner climbed to over 52,000 feet over Edwards Air Force Base in California, during a routine certification test flight.