high speed cruise

[alvcheng]

In August 1998, I took a flight from Beijing to Hong Kong in a 777 of China Southern Airlines. (I forgot whether it is 200 or 300.) It has delayed for almost an hour. When the airplane reached cruise altitude, I saw from my personal TV that the ground speed was more than 1000km/h. I think this is not real at first because a 777 cannot be so fast. However, is that possible if there is a very strong tail wind? Also, will it travel faster to minimize the delay?

[B777-400]

Yes, it is possible. I flew Frankfurt-Beijing in a LH747-400 a couple of years ago. The cruise speed peaked at 1080km/h I remember.

[nyc_spotter]

Wouldn't be the first time that I've left an hour late only to arrive 20 minutes early.

I also have done JFK-LIS in 4 hours and 58 minutes.

[aerpix]

Yes, this is possible, with strong tail winds. You have seen the indicated air speed (IAS) while true air speed (TAS) was probably something around 800-850 km/h. Likewise IAS can go down to 700 km/h or below in strong headwinds.

Regards,
Peter

[B777-400]

How do they measure IAS and TAS, and what causes the difference?

[Greg]

Indicated Airspeed and True Airspeed. they also measure Ground Speed. It's because pressure causes differences and it gets real technical but it's basically because of pressure. Hope that didn't confuse you further.

[Colin Parker]

If an aircraft is delayed, the crew can enter a higher Cost Index number into the FMC. This number tells the aircraft that you want to go faster, and it will accordingly, plan a new faster ECON speed to fly. This is better than the crew simply entering a higher Mach number to fly faster. The Cost Index is a number that takes into account various costs of being late, vs. fuel, vs. leasing costs etc. It is up to the company to decide whether to plan for a higher cost index flight or not. If it is no problem for the company to arrive late, then they won't. If there are connecting passengers, curfews etc, then they will allow a higher cost index to fly faster. Normal 777 CI for us is 60. A fast one would be 250. Anything much higher than 500 or so, and the plane cannot go any faster due to overspeed limits, however the FMC will take up to 9999.

If we want to fly slower because we don't want to arrive early (Airport not open yet, or slot times) then we can enter a CI of 0, and the aircraft will fly a lot more slowly.

[Richard]

That happend once on a Thai Airways 773 from Bangkok to Hong Kong a year ago. The flight took roughly about four hours and our speed stuck at around 380-420km/h.

[LH 340-600]

I was on a LH 747-400 from Los Angeles to Frankfurt and we were doing about 1000 km/h or so.
The slowest I can remember was from Windhoek to Frankfurt. We were doing 700 km/h as soon as we reached Italy and we still arrived on time in Frankfurt.