30 January 2014

Question For Any Pilots

Help...if anyone out there knows the answers I'd really appreciate it:

If the aircraft (my flight HAL457 from HNL to HND ) is flying into headwinds ranging from 50-175 mph, such that even though the indicated airspeed is as high as 580 mph but the net ground speed is as low as 380 mph, why not take a slightly different route or altitude?  We were between FL 360 to FL 380 for most of the flight.  Does the plane fly efficiently with this much headwind for so much of the flight?  From what I understand the return flight from Japan to Hawaii will take only about 6 to 7 hours so there's lots of sense in that. But 9 hours into headwinds that would lift a Cessna 172 up off the ground with zero ground speed?


aviatorhi said...

The indicated airspeed won't ever get as high at 580 mph (also it would be in knots, not mps, but I digress)...

Depending (mainly) on your Flight Level and other atmospheric conditions you'll end up with something like 240-320 KIAS (knots indicates airspeed; and the higher you are the lower the speed). Depending on the type of airplane the cruise "speed" will be anywhere between mach .74 and .94, a 767 would be around .80 to .82.

Anyway, now that I digressed all over the place... If you were going to Japan on the 29th or 30th you would have needed to fly 3-4 hours out of the way to get slightly more favorable winds for the crossing, all in all it would have ended up being a wash.

Anonymous said...

Generally, dispatch will choose the optimum level for the cruise. It's common in winter to have winds as you describe from the West from Hong Kong all the way up through Japan. Occasionally, shorter flights will end up as low as flight level 260 in order to take advantage of lower winds, thus shorter sector times. The good news is that the return from HND should be lightning fast with that winter tailwind.

Anonymous said...

Let's leave indicated airspeed out of this for now as it's basically just along for the ride e.g. at Mach .82 @ FL 360 KIAS is somewhere around 260 or so.

The A330 flight planned cruise airspeed is Mach .82. Dispatchers and pilots will discuss all options available prior to departure. Alternate routing and altitudes would be part of this discussion. The Jetstream where those high winds come from is normally very wide. It's hard for you know but it's entirely possible your flight was actually on an alternate route and flying at the optimal altitude as well.

Typically the A330 likes to get high and stay high as soon as possible. At higher altitudes the fuel burn is lower, at lower altitudes the TAS is higher so there is a trade off there.

Rest assured the cockpit crew did everything possible to minimize the strong headwinds you experienced as well as working with dispatch and other aircraft to keep the ride as smooth as possible.

MD-11 pilot said...

We go the most direct route.