Timetable and speeds

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shearder
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Timetable and speeds

Post by shearder » 02 May 2009, 07:47

Ok it's me again.

I have been quiet, no, VERY successful in terms of times on departure and arrival. However, what i notice is if i calculate distance, altitude, DEP and ARR times and the required airspeed to achieve being on time I am, more times than not, exceeding speed and constantly have an "Overspeed" warning if i want to make it on time. Secondly, it isn't the overspeed that is really the issue but adds to FUEL consumption. I flew a JHB to JFK via Dakar on the 30/04/2009 and I made it with not too much fuel left. Fuel usage is SERIOUS at those speeds. Am I doing something wrong? I use flight planner to plan the route using high altitude IFR to start then cancel ifr and use GPS for routing and a flight calculator for speed, distance etc etc. So timing is great with +/- 5 mins each way depending on traffic but I am concerned for the plane and fuel.

Any ideas? Thanks in advance.
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Re: Timetable and speeds

Post by FJ flyer » 02 May 2009, 08:49

What altitude are you cruising at?
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shearder
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Re: Timetable and speeds

Post by shearder » 02 May 2009, 15:58

Typically 28k - 30k feet.

Perhaps a little too high? hmmmmmmm
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Re: Timetable and speeds

Post by RatherBFlyin » 02 May 2009, 17:22

That's about right depending on the aircraft you are using. I find it odd though that you need to fly that fast, since the airlines typically pad their timetables to allow extra time for delays. What was a recent citypair that you flew between that had you having to overspeed your aircraft, and what aircraft did you use? Also, what was the flight number?

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shearder
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Re: Timetable and speeds

Post by shearder » 02 May 2009, 18:28

I flew between JNB and BUQ. flight SA8112 (SA Airlink) in ERJ135. Distance 481 miles flown 13k feet. Time is 1hr 20mins to be on time not GPS direct. Speed was approx 360kias.

Am I maybe doing something wrong? should i go direct?
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Re: Timetable and speeds

Post by FJ flyer » 02 May 2009, 22:26

The indicator (on the nav log) saying you should be flying at 360 knots is the ground speed, not the airspeed. The speed in the bottom left hand corner of the GPS is the ground speed.

Also, if you were flying to Dakar I would fly at about 35000 feet, and cruising higher will boost your ground speed.


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Re: Timetable and speeds

Post by RatherBFlyin » 03 May 2009, 04:35

The key with turbine-powered aircraft is to fly as high as possible where the engines are the most fuel efficient. You will also get a higher ground speed for the same indicated airspeed (assuming you don't have a monster headwind, of course).

In an E135 on a leg about 500nm, I would have gone up to somewhere around FL250. Normal cruise speed in an E135 is around M076, but I would have had it around M072 at that altitude. That would equate to somewhere around 280-300 kias, but a ground speed of approximately 350-400 knots.

One other thing to keep in mind (though it really only matters if you are flying online). Flight levels in South Africa start at 8,000 feet instead of 18,000 feet. I'm not sure where they start in Zimbabwe.

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shearder
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Re: Timetable and speeds

Post by shearder » 03 May 2009, 09:40

I really appreciate the answers and feedback guys.

I will fly higher on my next flight and see how it goes. I wil do a little homework on these plans some more and get the service ceiling and fly as high as logically possible - if that makes sense.

I will keep it posted here next time incl speed and fuel.
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Re: Timetable and speeds

Post by COA413 » 04 May 2009, 03:04

You need to fly higher. A few examples:
1) I flew from LHR to AMS today using an A319. The trip is just over 200 nautical miles, and I cruised to FL220. I used my FMC-generated cruise speed, which was 319 KIAS, which equated to around M0.70. Because the aircraft was so lightweight (not a lot of fuel for a 200 mile trip where that aircraft has a 3,700 mile range...), I was able to quickly climb to FL220. At first, it seems a little high, but a very quick climb up to FL220 and the fact that you don't need to start your descent until you are 60-75 miles from Amsterdam, it worked out beautifully.

2) ExpressJet 2333 from Cleveland to O'Hare flew at FL260 today. The total flight distance = roughly 275 nautical miles. Again, a cruise speed of around 300-315 would be appropriate.

You said that you typically fly between FL280 and FL300, which is low. Depending on the aircraft, I usually use FL330 as a minimum. Unless I am flying a heavy 747 or 777, I almost always exceed FL330. For a 500 mile trip in an ERJ, I would say either FL340 or FL350 would be good. I don't remember if the ERJ would have a tough time getting up to FL350, but I would guess it should be able to do so. Anything about 350 or 375 miles and above, there is no reason to cruise lower than FL320. Those are regular flights, and you should always have more than enough time to get up to a regular cruise speed.

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