User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

TOC/TOD determination before FMS

Wed Jan 02, 2019 8:37 pm

Hello,

I was wondering how airliner crews, such as those who flown 707's in the early 1960's, determined their TOC and TOD points without FMS. Of course, one can calculate them in a nav log and use something like a DME distance to determine a fix that can be used to start a descent, for example. Neverthless, I would like to know if it was indeed done in such a manner, or if they used something else.

Thanks since now the attention;

Marcelo Jenisch.
 
GalaxyFlyer
Posts: 1961
Joined: Fri Jan 01, 2016 4:44 am

Re: TOC/TOD determination before FMS

Wed Jan 02, 2019 9:38 pm

TOD was pretty much three times your altitude plus 10 adjusted for the winds. Nobody cared about TOC unless ATC asked, “can you be level at xxx” and divided the altitude change by the ROC and added some to account for climb rate slowing. FMS doesn’t do anything more than we did in our heads, just quicker, continuously and more accurately. Whenever I used VNAV I already had an idea what I needed to do.

I often just lowered the nose by three degrees from cruise pitch to start down after I did the 3 times calculation.

GF
 
thepinkmachine
Posts: 304
Joined: Tue Apr 28, 2015 4:43 pm

Re: TOC/TOD determination before FMS

Wed Jan 02, 2019 10:42 pm

GF’s Works pretty well till today - actually with a bit of practice the mental calculations done this way may be more accurate than whatever VNAV comes up with...

Just on the newest jets it’s altitude x4 instead of 3 - they tend to glide like crazy... :)
 
747Whale
Posts: 271
Joined: Fri Dec 07, 2018 7:41 pm

Re: TOC/TOD determination before FMS

Wed Jan 02, 2019 10:45 pm

I don't always descend or climb according to the FMS. I'm flying the airplane, not the computer. Especially in cases when there's a discontinuity, the FMS may have one thing in mind, but getting down may be another. As GalaxyFlyer noted, a 3:1 descent is normal, and allow an extra ten miles to slow down or as a cushion, as needed. If I know that my destination is at 3,000 above sea level and I'm at 35,000, I need to descent 32,000'. 3 X 32 is 96 miles, round it to 100 and add ten. 110 miles will be the top of descent point.

This may be tempered by crossing restrictions, etc.

If I plan on 300 knots for the descent, that's moving 5 miles a minute. 110/5 is 22 minutes. 22 minutes to descend 32,000' is 1454. Round up to 1,500 fpm. If I could maintain 300 knots until the airport, then 1500 would get me down on time. I'll be slowing. below 10,000 which means it will take a little longer to reach the field. 1,500 is close enough, adjusted up or down as needed. Somewhere in there, crossing restrictions will probably alter those numbers, but they're good enough for planning ahead.
 
User avatar
Starlionblue
Posts: 18826
Joined: Fri Feb 27, 2004 9:54 pm

Re: TOC/TOD determination before FMS

Thu Jan 03, 2019 1:25 am

Pilots are still expected to calculate mentally the descent point based on altitude and track miles to go. The calculation works as a gross error check for the FM. Besides, the FM only knows the inputted wind data, which may or may not be completely accurate.

Rules of thumb on the A330 and A350.
- From cruise, track miles to go is 4x altitude.
- Below 15000 feet track miles to go is 3x altitude + 1 mile for every 10 knots above 150.
- Once on the glideslope, 3x altitude.
Adjust for wind.

You can also sometimes need mental maths to calculate your descent rate. Say you're at 5000 feet and need to intercept the localiser in 6 miles at 3200 feet. If you're at Flaps 1 doing 180 knots, that's 3 miles a minute, so those 6 miles will take two minutes with no wind. V/S -900. However you might want a bit of margin (better to intercept the glide from below than above), so V/S -1000 might be more appropriate. Adjust for tail or headwind as needed.
Last edited by Starlionblue on Thu Jan 03, 2019 1:36 am, edited 1 time in total.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
GalaxyFlyer
Posts: 1961
Joined: Fri Jan 01, 2016 4:44 am

Re: TOC/TOD determination before FMS

Thu Jan 03, 2019 1:30 am

True on glide, the CL605 could easily make it 3X, the Global was about 4x.



Gf
 
e38
Posts: 561
Joined: Sun May 04, 2008 10:09 pm

Re: TOC/TOD determination before FMS

Thu Jan 03, 2019 2:40 am

Marcelo, to continue the planning described by 747Whale in Reply #4, in my descent planning (in the United States), I always plan to cross 30 miles from the airport at 10,000 feet and 250 KIAS. So, I normally calculate my planning on Cruise Altitude - 10,000 feet X 3; then add 30 miles to that plus a mile for every 10 knots to decelerate to 250.
I think many pilots have their own techniques, but generally they involve the 3:1 or 3.5:1 rule.

e38
 
User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

Re: TOC/TOD determination before FMS

Thu Jan 03, 2019 11:22 pm

e38 wrote:
but generally they involve the 3:1 or 3.5:1 rule.


So, the feet (in thousands) needed to be lost should be multiplied by 3 in order to know the distance in nautical miles one should start the descent. As 747Whale examplified: 32,000 ft (32) multiplied by 3 would be 96 mile. In his example, it would be rounded to 100 to simplify the math and the extra 10 miles (plus or less I supose) GalaxyFlyer mentioned are intended to compensate for any winds. I'm correct with everything?
 
GalaxyFlyer
Posts: 1961
Joined: Fri Jan 01, 2016 4:44 am

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 1:05 am

Yes, if you strong tailwind, you’ll need to add some miles. There’s probably a gouge, but I just used my groundspeed in NM/minute times 300 to estimate my needed ROD descent. So, if 100 miles out in your example, and was making 540 knots (9 miles per minute); I’d aim for 2700 fpm, probably 3,000 fpm to be sure. That assumes, in idle, the plane can descend at 3,000 fpm and maintain a reasonable speed which is why newer planes need to start down earlier. Using the 4 times rule you’d start down earlier, about 120 miles out. 3x is 333 ft/nm while 4x is 250 ft/no.


GF
 
User avatar
Starlionblue
Posts: 18826
Joined: Fri Feb 27, 2004 9:54 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 3:30 am

MarceloJenisch wrote:
e38 wrote:
but generally they involve the 3:1 or 3.5:1 rule.


So, the feet (in thousands) needed to be lost should be multiplied by 3 in order to know the distance in nautical miles one should start the descent. As 747Whale examplified: 32,000 ft (32) multiplied by 3 would be 96 mile. In his example, it would be rounded to 100 to simplify the math and the extra 10 miles (plus or less I supose) GalaxyFlyer mentioned are intended to compensate for any winds. I'm correct with everything?


Correct. At 100 miles away it doesn't have to be super accurate. Better to add a few miles and be 1000 feet low than the opposite, but then again that far away there's plenty of room to adjust. The FM would handle a few miles early or late no problem, or you could increase speed if you were high to descend a bit faster. If you're at 10000 feet 20 miles out, that's a whole other story.

As mentioned on many modern planes it is more like 4 miles per thousand feet. You'd start descending around 128 miles.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Max Q
Posts: 6968
Joined: Wed May 09, 2001 12:40 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 6:50 am

Three times your altitude + ten miles to slow worked well on the older aircraft, one mile less for every 10 knots of headwind and one more for every 10 knots of tailwind


As you descend you watch your DME every 1000 feet to see if your profile is working and adjust with lower or higher rate of descent as necessary


If you get way behind on your descent and speed is getting close to VMO you may need speed brakes to meet your crossing restrictions and / or be stabilized with engines spooled at 1000’



Conversely if you find yourself low on your profile and are slowing below normal speed you may need a little power in the descent, better doing that than leveling off too low, too far out and using a lot of fuel at low altitude



As far as efficiency was concerned ‘better be high and use speed brakes than low and use power’


Still true on modern aircraft but the proper use and monitoring of VNAV takes care of most descent planning these days


As stated you should still keep any eye on it with a basic profile in mind though


Descent planning and the accomplishment of such was actually a lot of fun in the B727 / MD80 days, doing it smoothly and getting it right was very satisfying
The best contribution to safety is a competent Pilot.
 
User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 10:33 am

Max Q wrote:
Descent planning and the accomplishment of such was actually a lot of fun in the B727 / MD80 days, doing it smoothly and getting it right was very satisfying


I can imagine. Not for nothing I was so curious about how the things were done in those days. :D
 
User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 10:56 am

Guys, I was also wondering if the techniques you mentioned can also be employed in general aviation. For example, in my nav log calculations for a real flight in a Cessna 172, in order to descent from 8000 ft to 4000', I found the descent should be started 9 nm away (I use a 500 fpm descent rate and 70 kts). By using your airliner method, I guess the 4000 ft need to be lost would be mutiplied by 2 (after all, it's a C-172), and the result would be 8 nm (4x2 = 8), which is a number extremely close to the 9 nm I found by doing the calculations with a pencil using the mathematical rule of three. In your opinions, this can be employed satisfactorily in general aviation as well? Ah, and needless so say: I'm always careful about employing anything that I read in a forum in real life situations. It's just a curiosity if the same calculations can be also employed in GA. ;)
 
thepinkmachine
Posts: 304
Joined: Tue Apr 28, 2015 4:43 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 11:31 am

They can. However in an unpressurized a/c you also need to account for cabin descent rate for pax comfort - depending who you carry of course.

In my GA time I was just aiming form 500ft/min descent based on time to destination. Eg. When flying at 10000 ft, i’d Start the descent 20 minutes before landing.

Piston powered airplanes are less sensitive to altitude and also you don’t really do glide and idle descents like in jets - so using those fancy jet calculations is a bit of overkill... They will work, though :)
 
User avatar
Starlionblue
Posts: 18826
Joined: Fri Feb 27, 2004 9:54 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 12:05 pm

You can certainly do descent calculations in GA planes, and my instructors expected me to at least have an idea. But light pistons don't glide nearly as well as swept wing jets, plus you don't need to lose that much altitude. Besides, that big spinning thing in the front is a great airbrake if you throttle back.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 1:00 pm

thepinkmachine wrote:
They can. However in an unpressurized a/c you also need to account for cabin descent rate for pax comfort - depending who you carry of course.


Oh, certainly. A GA aircraft would not normally fly at high altitude. For example, the 1500 ft/min descent rate 747Whale mentioned in his calculation example would probably hurt one's ears if the aircraft was not pressurized. :D

so using those fancy jet calculations is a bit of overkill... They will work, though :)


I'm finishing the comercial pilot course here in Brazil. Since my private pilot course I was taught to use a nav log in each cross-country flight. Before the flight, I calculate all the legs in order to have the ETO for each of them. Of course, It does not always work as planned, since ATC can direct me to do different things, but neverthless with the nav log I can provide estimates to ATC and keep a better track of what I'm doing. With GPS and DME things become much easier certainly, but I still take my nav log in every flight.

Anyway, I would like to thank you all for your attention. I was curious to know how the pilots who flown aircraft like the '707 and the '727 planned their descents and was surprised to know that even nowadays pilots still do mental calculations to complement the FMS, just like the one's who flown the classical aircraft I mentioned did routinely in the past.

Cheers.
 
gloom
Posts: 249
Joined: Thu Jun 30, 2016 4:24 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 1:10 pm

A question for Starlionblue, or other people flying 350/787:
From your experience, and some specific approaches - how often does this better L/D ratio cause problems on approaches? I remember myself flying on COSMON approach to rwy 16L at RJAA, on AY 359, and I think much of the approach (more than half, from what I recall) was done on airbrakes. It is a steep approach indeed, with some "not below" restrictions, as pilots explained to me. How often is that a problem occuring only for those newer planes, with particularly low drag?

Cheers,
Adam
 
User avatar
Starlionblue
Posts: 18826
Joined: Fri Feb 27, 2004 9:54 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 2:51 pm

gloom wrote:
A question for Starlionblue, or other people flying 350/787:
From your experience, and some specific approaches - how often does this better L/D ratio cause problems on approaches? I remember myself flying on COSMON approach to rwy 16L at RJAA, on AY 359, and I think much of the approach (more than half, from what I recall) was done on airbrakes. It is a steep approach indeed, with some "not below" restrictions, as pilots explained to me. How often is that a problem occuring only for those newer planes, with particularly low drag?

Cheers,
Adam


It's not really a "problem" more than it is on the A330 as long as the pilots are aware of it. You can "go down or slow down but not both". And if you're on the glideslope at Flaps 2 the plane might still tend to accelerate. Be configured appropriately.

The use of speedbrake is more often due to ATC restrictions and/or shortcuts more than poor profile management. You can be conservative but ATC might give you a 5-10 mile shortcut to facilitate traffic flow. And now you need to use speedbrake. In an ideal world you'd glide down to 2500 feet AGL on idle thrust but in reality, there is other traffic around that needs to be accounted for.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
thepinkmachine
Posts: 304
Joined: Tue Apr 28, 2015 4:43 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 4:21 pm

The 787 glides very well, but it has very efficient speedbrakes, so once you extend them it turns into a brick... :)

Also, it decelerates surprisingly well - no problem to lose speed, contrary to eg. A330. Also, it has autodrag function, which helps to decelerate on approach.

All in all, you need to start descent earlier than on older jets, bu otherwise it is no problem.
 
User avatar
longhauler
Posts: 5982
Joined: Sat Mar 06, 2004 12:00 am

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 5:17 pm

Also something to add to the old "non FMS" descent planning, is that after the initial descent was started, one used to watch how it was going on the way down.

Remember, if it didn't have FMS, you likely couldn't tell what the wind was doing as well. (At least in the last non FMS aircraft I flew, the 737-200). So you'd see how many miles you covered per 1000' of descent, and would adjust your speed. Not losing altitude quick enough, then nudge the speed from 300 to 320 .... dropping like a brick, bring it back from 300 to 280. (Which ironically enough is what the FMS does, if it encounters unplanned winds).

It didn't take very long before you got pretty good at it and it became a source of pride to not have to adjust thrust until configuring with the gear and final flaps in the last 3000' of descent.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!
 
User avatar
MarceloJenisch
Topic Author
Posts: 6
Joined: Tue Jan 01, 2019 12:35 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 8:16 pm

longhauler wrote:
Remember, if it didn't have FMS, you likely couldn't tell what the wind was doing as well. (At least in the last non FMS aircraft I flew, the 737-200).


Indeed. I can see an exception in the form of the INS. Here's a demonstration video of the American Airlines 707 using it:

https://www.youtube.com/watch?v=r0IfRDUPteE

At 04:12, the wind display feature is demonstrated.
 
GalaxyFlyer
Posts: 1961
Joined: Fri Jan 01, 2016 4:44 am

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 8:45 pm

In fact, with some mental gymnastics, one do a fair job of flying using known pitch and power relationships. We did it AF Instrument School without any pressure instruments, but the mental math was challenging. Every degree of pitch change times miles/minute times 100 equals change in ROD or ROC. For example, M.80 equals 8 nm/min TAS times 2 degree change in pitch equals 1600 fpm up or down, changing thrust to maintain the Mach.

Using an HSI, you make a good guess on the wind in level flight. Hack the clock for a minute, use DME to see the miles flown in the minute. Look at the crab angle to hold course (VOR NAV), number of degrees of crab times TAS nm/min equals crosswind component. Little vector analysis on the HSI, voila the wind. Admittedly, pretty hard to do in a descent, but good enough for the weather report.

GF
 
747Whale
Posts: 271
Joined: Fri Dec 07, 2018 7:41 pm

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 9:31 pm

longhauler wrote:
Remember, if it didn't have FMS, you likely couldn't tell what the wind was doing as well.


Of course you can tell what the winds are doing. Basic navigation, basic dead reckoning, and it's something that one can and should do in anything from a Cessna 172 on up. No different. The Cessna doesn't have an FMS, either.

I think there's a lot that's not apparent to the magenta line generation(s), that's really just basic airmanship.
 
User avatar
longhauler
Posts: 5982
Joined: Sat Mar 06, 2004 12:00 am

Re: TOC/TOD determination before FMS

Fri Jan 04, 2019 9:52 pm

747Whale wrote:
longhauler wrote:
Remember, if it didn't have FMS, you likely couldn't tell what the wind was doing as well.


Of course you can tell what the winds are doing. Basic navigation, basic dead reckoning, and it's something that one can and should do in anything from a Cessna 172 on up. No different. The Cessna doesn't have an FMS, either.

I think there's a lot that's not apparent to the magenta line generation(s), that's really just basic airmanship.

Really? As you are gliding down at 300 knots in smooth conditions, you can tell if you have a 30 knot tailwind vice a 30 knot headwind??? Other than calculating the altitude lost compared to distance travelled as I mentioned before, I can't imagine how. Trust me, I am defintely NOT the magenta line generation. And I am only talking headwind/tailwind component here with regard to the OP's TOC/TOD determination.

MarceloJenisch wrote:
Indeed. I can see an exception in the form of the INS.

Yes, we had INS in the A300 and still did manual descent calculations. You are right, a wind readout was possible, but we normally kept the trk/dev function displayed as it was being used for navigation.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!

Who is online

Users browsing this forum: HAWKXP and 20 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos