Position: 50 miles west of Billings, MtAltitude: 34,000 feet
Groundspeed: 480 mph (417 kts)
Pax-on-board: 150
Destination: KSEA (Sea-Tac)
Maximum landing weight is still 2,600 pounds away. That, in itself, is interesting since we have been airborne five hours. We rolled out of the sack at 0200 hrs. (circadian time) and will arrive, knock on wood, at 1100 hrs.
Fuel burn -vs- landing weight... Fi-Fi's powerful nav computers are whispering to me, "Don't worry captain, we've got this under control."
Maybe... All the same, my stubby No.#2 pencil and pocket calculator are in the stand-by mode.
The Electric Jet has an IFR (instrument flight rules) range of about 2,300 nautical miles, plus or minus a few. That means that she can fly a leg of 2,300 nautical miles, hold a few minutes (or make one approach), then bug out to an alternate 200 miles away. This morning, our leg is 2,250 miles with light winds. The performance engineers (bless 'em) add miles, instead of time, for headwinds. With light and variable winds at altitude, our fuel burn miles remain steady at 2,250.
Even so, we have to be very careful with the fuel load, since we are at the IFR limit. We fly these aircraft at the performance limits on a regular basis, something I would never do with a personal aircraft.
Imagine, if you will; I have won the lottery, i.e., the Big One... I can now afford my very own A320. I will have my wife's nick-name painted on the nose and hire my favorite flight attendants to crew the cabin (on their days off, of course...) at $500 per hour. Why don't we load my new A320 to max gross weight with friends and family and fly it to an exotic destination with a short runway at the end of the fuel range? How about some nasty weather at our arrival time; blowing sand and thunderstorms?
Say again, please... Uh, I don't think so. Not in my new airplane.
Back to reality... Well, we can all fantasize, right?
Air Traffic Control offers a more direct routing, but I decide to remain on the flight plan for the wind forecast. Believe it or not, a direct route will (sometimes) burn more fuel, something we cannot afford this morning.
How much do we actually weigh? No one really knows. The gross take-off weight is calculated using average pax and bag weights, plus cargo weights of unknown accuracy, so it is an educated guess. We could easily weigh plus or minus 2,000 pounds (or more) from calculated weight. The only thing that matters is the landing weight (zero fuel weight minus fuel burn) which is recorded on the optical disk, whether or not it has any basis in reality. Fi-Fi can actually sense her own weight, which can be 10,000 pounds (or more) different than our load sheet. Is that weight accurate? Depends on which expert you talk to... Our performance engineers seem to think theirs is closer to the mark, and I agree. Still, it is interesting to look deep into Fi-Fi's mind and see what her little electric brain cells are thinking. She is an amazing flying machine.
This is day number two of a four day trip. Early tomorrow morning, it is back to the eastern edge of the Empire.
Life on the Line continues...
27 comments:
Why do contrails look black from altitude?
anonymous 0943- sun angle, Plexiglas and lighting, I would guess.
Hi Dave. I read that the A320 has a range of 3000nm at maximum gross weight. Could you explain what happens to your other 700nm in this case. Does that account for your alternate fuel and your minimum landing fuel? So for example a much shorter flight from KPHX to KPDX, you could load extra fuel to hold or try a few approaches if you expected poor weather in KPDX where as in this case you didn't have that luxury. Thanks.
anonymous 1022- I would guess that would be maximum fuel load, no wind, fuel exhaustion; still, I think 3000 nm is a bit of a stretch. In real life ops, 2300 nm with a bit of holding fuel, approach fuel, alternate fuel, is about it. That is what IFR range is all about.
"The only thing that matters is the landing weight (zero fuel weight minus fuel burn)"
This quote makes me wonder...I would have said landing weight = Takeoff weight minus fuel burn...Is it an writing error, or is it me who is out ?
Hi Dave - Your blog is very interesting. Having stumbled across this a while ago I have now read most of your back catalogue. I guess like a few of your readers I'm a bit of a microsoft FS fan and to be able to read your 'technical titbits' is nerd heaven :)
cheers from sunny blighty
Would like to hear more about what aircraft you'd have in your personal fleet, and how you'd fly them :0)
Starting PPL training in two weeks. Consider yourself motivational!!
What "zeroes" your circadian time?
I go back and forth in North America for business a lot and usually find my personal body clock is locked to Eastern time no matter where I am.
And if I'm home in Phoenix, 2-3 weeks are required to "sleep in" as late as 5:00AM Mountain time.
As usual, a pleasure!
Hi Dave!
Now when I drive home from work & see a plane in the sky, makes me wonder if you are at the controls!
Moving to FL in roughly 3 weeks, so I'll have some catching up to do for your posts.
Always a reading pleasure! Stay safe!!
When you win the lottery, give me a shout. For $500 an hour I'll crew your plane, and I'll even shine your shoes for you!
On a side note, I saw something about a suggestion of weighing passengers as well as their bags to better estimate the fuel needs. In that case, I should get a discounted ticket, given that I weigh a lot less than the airlines' "guesstimate" of passenger weights ... do you reckon such a thing will ever happen?
Why don't airliners have force sensors in the landing gear? They would automatically measure the weight AND calculate balance. This seems so simple. I must be missing something.
Also, couldn't a nav computer guess at the plane's Mass by noting the Acceleration that resulted from a given Force? I seem to recall f=ma is still a valid guess... any subtle changes in apparent airspeed could be used, and the inertial sensors would record the acceleration. Or the A resulting from a change in F from the engines? Or you could use the angular acceleration that resulted from a given force on a control surface, right?
What am I missing?
@Andy: AFAIK most planes already have force sensors in the undercarriage.
They generate the "weight on wheels" signal that is used for several purposes, for instance generating a "confirmed on ground" signal that lets the thrust reversers deploy.
I'm not sure whether they are really accurate though, most of the time they are used as binary (yes/no) signals.
It really is amazing what the FMC in a modern aircraft is capable of. I imagine that it can determine the weight by taking inputs from a multitude of sensors and running them through a very complex algorithm that spits out gross weight. On the ancient aircraft that I fly on the only way it knows the weight is fuel+operating weight. Although the accuracy of this method should be accurate since the plane is weighed regularly.
"Why don't airliners have force sensors in the landing gear?"
For the same reason you don't weigh the plane using big scales on the ramp. The wings will be producing lift and cause the scales to under-read. There are few times in the day when the windspeed is truly zero- usually dawn and dusk, so you'd end up with a very complex system that could not be used very often.
It has been discussed in detail here:
http://www.airliners.net/aviation-forums/tech_ops/read.main/252454/
And basically says that adding a tonne of weight really wouldn't cause the landing gear struts to notice it, and that tonne can make all the difference. I would suggest an accurate weighbridge type thing at every gate (or perhaps a communal one?) that measures the aircraft as a whole, but the expense and complexity would be enormous. Plus... if they got it wrong, the airport would be liable, and aviation seems to be about keeping your liability to a minimum! (or 'safety' as it's usually called...).
How many hours flying do you each month, Captain Dave?
A lot of people from aviation industry are on twitter as well, do you intend to join in?
I spent the last two weeks devouring Sulakos's blog and his love story with the lovely lisa and your ongoing love triangle with the wife of your youth and the french cutie Fi-Fi (does the wife of your youth know ?), that followed by Aviatrix's history and the hillarious tales of Glen of Rant Air Fame. You guys all make the day of someone who, because of fear of flying can't appreciate the joy of airtravel. Good luck to you all air(wo)men :-)
Dave...Another great post. Longtime reader and very rare commenter just letting you know how much so many of us enjoy your blog. Safe flying...
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Let's say a prayer for the missing Air France flight. Doesn't look good.
seems unusual to me for a new aircraft to be brought down by turbulence? any thoughts dave, never heard something as modern as the the 330 crashing in this way
Air France 447
What would be the design reasoning to enable an aircraft to generate an automatic message, such as AF447? Quoting here from AP story this morning, the plane "sent an automatic message...reporting electrical failure and a loss of cabin pressure." Clearly loss of primary electrical power and cabin pressure means something is terribly wrong, but why the automatic message? Is the assumption that under such circumstances the aircraft is likely to be in such dire straits that emergency assistance is probably required? Is this unique to fly-by-wire a/c such as modern Airbus family, or do other a/c (i.e., Boeing) also offer such capabilities?
Bob in Minnesota
AF 447
Please ignore my previous comment on this post. New AF447 post just came up, will repost there.
Thanks
Bob in Minnesota
Dave,
Last night I posted a request to be able to use your photo entitled "The Canyon" on your blog. However, my wife (who recommended your blog to me) said that you probably wouldn't see it and be able to respond any time soon. So today I went to a commercial photo site and found a photo that I think will work.
So I no longer need to ask for the use of your photo.
But let me commend you on the quality of your site and your photography. Wonderful job!
Dick Donovan
Dave,
I love your photograph entitled "The Canyon." I am redesigning my web site, www.lectionary.org. Any possibility that I could use your photo? I would need to get a signed release.
Dick Donovan
dick@sermonwriter.com
P.S. Don't reply to my gmail email address, because I never check it.
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