Does ATC know our TOD?

[Larry in TN]

Any of you ever fly a DC-8? My I'll never do that again story as a Controller was the day I discovered, the hard way, that DC-8's don't have them and can't down fer sheet when you really need it.

Before the CFM-56 reengine, the DC8's would reverse the 2 inboard engines to slow down and descend simultaneously. A captain told me with the new engines, there was a lot more residual thrust at idle, so it made for a really bumpy ride. Since the passengers didn't like it, they wouldn't do it anymore.

I've flown the DC8-61/62/63 as FE and the DC8-62/71/72/73 as pilot.

You could reverse the inbounds on all of them. Loud and lots of vibration. With passengers, I'd never do it without warning them first. It was not something that was normally done, if it could be avoided. Come back to flight-idle and point the nose down and it descended a lot faster than the modern jets do.

The DC8 does have spoilers--ground spoilers. It has no speed brakes which, on most jets, are the same panels when extended in flight. The inflight speed brakes would be limited to a lower angle in flight as compared to the extension of the same panels on the ground. The ground spoilers would also have some additional ground-only panels on many airplanes.

Good ol' DC8. Nothing like burning 15,000 pounds (~2240 gallons) of Jet A in your first hour of the flight! Depending on the wing, you'd have 8 to 10 fuel tanks.

If you ever get bored, read about how the intermediate-level fuel transfer system works.

 

[PastZTL]

I've flown the DC8-61/62/63 as FE and the DC8-62/71/72/73 as pilot.

You could reverse the inbounds on all of them. Loud and lots of vibration. With passengers, I'd never do it without warning them first. It was not something that was normally done, if it could be avoided. Come back to flight-idle and point the nose down and it descended a lot faster than the modern jets do.

The DC8 does have spoilers--ground spoilers. It has no speed brakes which, on most jets, are the same panels when extended in flight. The inflight speed brakes would be limited to a lower angle in flight as compared to the extension of the same panels on the ground. The ground spoilers would also have some additional ground-only panels on many airplanes.

Good ol' DC8. Nothing like burning 15,000 pounds (~2240 gallons) of Jet A in your first hour of the flight! Depending on the wing, you'd have 8 to 10 fuel tanks.

If you ever get bored, read about how the intermediate-level fuel transfer system works.

My favorite airliner of all time.

 

[hindsight2020]

What's a normal Rate of Descent for a B-52?

2000-3000fpm with zero wind. Based on a 220-240KIAS and 5 deg nose low as the standard enroute descent. Could be steepened as required, power as required to maintain 220-240 indicated. IOW, run-o-the-mill big lumbering airplane numbers. It had 99 weird things, but climb and descent gradients wasn't one of them.

Speeddown was an emergency defensive maneuver (and a stupid one at that, in the age of look-down shoot-down, and which took the lives of RAIDR21), but that involved throwing all the drag out there and the gear for good measure.

 

[NealRomeoGolf]

Apparently the TOD going into Billings last fall was the runway threshold. I'd have to go back and listen to the recording. I think they were keeping me high for an inbound biz jet. The PA32 drops like a brick and won't pick up speed if you do it right.

 

[luvflyin]

I've flown the DC8-61/62/63 as FE and the DC8-62/71/72/73 as pilot.

You could reverse the inbounds on all of them. Loud and lots of vibration. With passengers, I'd never do it without warning them first. It was not something that was normally done, if it could be avoided. Come back to flight-idle and point the nose down and it descended a lot faster than the modern jets do.

The DC8 does have spoilers--ground spoilers. It has no speed brakes which, on most jets, are the same panels when extended in flight. The inflight speed brakes would be limited to a lower angle in flight as compared to the extension of the same panels on the ground. The ground spoilers would also have some additional ground-only panels on many airplanes.

Good ol' DC8. Nothing like burning 15,000 pounds (~2240 gallons) of Jet A in your first hour of the flight! Depending on the wing, you'd have 8 to 10 fuel tanks.

If you ever get bored, read about how the intermediate-level fuel transfer system works.

Could you “…Come back to flight-idle and point the nose down and it descended a lot faster than the modern jets do...” without increasing forward speed? About what rate of descent could you get? Compare it not to modern jets, but those of the the era, say mid 90’s. The shorter haul type stuff. 727, 737, MD80

 

[Larry in TN]

Could you “…Come back to flight-idle and point the nose down and it descended a lot faster than the modern jets do...” without increasing forward speed? About what rate of descent could you get? Compare it not to modern jets, but those of the the era, say mid 90’s. The shorter haul type stuff. 727, 737, MD80

It's the newer engines that have a lot more residual thrust that makes the difference. The older airframes also had more drag.

When you point the nose down, it'll go faster. With the newer engines and slicker aerodynamics, you run into the barber pole much quicker.

The 737 has a Mmo/Vmo of M.82/340KIAS. I'll set an airspeed limit of 300KIAS for the descent because that leaves me more buffer to "fix" the descent profile if we get behind. At the top-of-descent, you can descend pretty fast in the thinner air. At lower altitudes, keeping the speed low becomes more challenging.

VNAV calculates a descent path based on your descent speed schedule and any altitude and airspeed constraints in the flight plan. A higher Mach/airspeed results in a steeper descent angle. By limiting that to M.80/300, the descent path isn't as steep and I have room to increase speed and steepen the path if needed. Also, if ATC slows me on the descent (common for spacing), suddenly the descent path at that speed is shallower and I'm suddenly way behind. Speed brakes only do so much.

It's been over 10 years since I last flew the DC8, and even longer since the DC9. I don't remember the specific numbers. The DC9 would do a 2:1 profile with high-speed and speed brakes. Also, it had a 300KIAS gear speed and 280KIAS limit for Slats extended, Flaps 5.

 

[luvflyin]

It's the newer engines that have a lot more residual thrust that makes the difference. The older airframes also had more drag.

When you point the nose down, it'll go faster. With the newer engines and slicker aerodynamics, you run into the barber pole much quicker.

The 737 has a Mmo/Vmo of M.82/340KIAS. I'll set an airspeed limit of 300KIAS for the descent because that leaves me more buffer to "fix" the descent profile if we get behind. At the top-of-descent, you can descend pretty fast in the thinner air. At lower altitudes, keeping the speed low becomes more challenging.

VNAV calculates a descent path based on your descent speed schedule and any altitude and airspeed constraints in the flight plan. A higher Mach/airspeed results in a steeper descent angle. By limiting that to M.80/300, the descent path isn't as steep and I have room to increase speed and steepen the path if needed. Also, if ATC slows me on the descent (common for spacing), suddenly the descent path at that speed is shallower and I'm suddenly way behind. Speed brakes only do so much.

It's been over 10 years since I last flew the DC8, and even longer since the DC9. I don't remember the specific numbers. The DC9 would do a 2:1 profile with high-speed and speed brakes. Also, it had a 300KIAS gear speed and 280KIAS limit for Slats extended, Flaps 5.

Suppose you’re in one of the newer 8’s at 370 doing .82. You get reduce to .74 then descend, transition at 280 kts and hold it. How long does the reduction take and what rate of descent can you get.

 

[Larry in TN]

Suppose you’re in one of the newer 8’s at 370 doing .82. You get reduce to .74 then descend, transition at 280 kts and hold it. How long does the reduction take and what rate of descent can you get.

Rule of thumb is 1nm per 10 knots of speed reduction. I don't have a quick gouge for converting that to Mach. I'm guessing it's something around a 40 to 50 KIAS reduction.

The problem is that the .74/280 descent profile is shallower than what I would have planned so if that speed assignment came late, I may already be well above profile.

FWIW, there is no "newer" DC8. The CFM-engined DC8s didn't come off the assembly line. They were DC8-61/62/63 aircraft that were re-engined and re-named DC8-71/72/73.

The CFMs has more residual thrust at flight-idle than the Pratts (JT3B) so you had to pay more attention to your profile.

 

[DesertNomad]

How does ATC determine when it’s time to give us our initial descent while IFR? I assume there must be some sort of algorithm that indicates when they need to start descending an aircraft in cruise, so they’ll get down in time to make their intending point of landing without any excessive descents or 360’s to lose altitude. How’s it work?

going into Page, AZ from the west, Denver Center assumes you can drop from 13,000 to 6,000 in about two miles. Haha

 

[EdFred]

going into Page, AZ from the west, Denver Center assumes you can drop from 13,000 to 6,000 in about two miles. Haha

The reason spins were invented.

 

[orca64]

Yes.

You might investigate how the AEF penetrated weather after combat patrols in France 100+ years ago.

interesting reading.

 

[midlifeflyer]

Experience.

Late to this party but going back to page 1, this is pretty much the answer.

No, they don't know the TOD you would like. Whether they realize that your non-pressurized piston single isn't a good candidate for a 2000 foot per minute descent comes with experience. Asking for lower when we feel the need is one of those things we need to be proactive about.

 

[Skinnybird]

How does ATC determine when it’s time to give us our initial descent while IFR? I assume there must be some sort of algorithm that indicates when they need to start descending an aircraft in cruise, so they’ll get down in time to make their intending point of landing without any excessive descents or 360’s to lose altitude. How’s it work?

I always figured they had the lowest seniority controller(s) walk the runway before each shift and police any TOD they found...

 

[Rockymountain]

I’ve never flown an airplane that lets you go down and slow down.

The beauty of a turboprop. Here we are 12.5 degrees nose down, 2250 fpm and slowing. I think we were 3 nm away from the field at 8000 ft MSL, or 3500 ft. AGL, and greased the landing at Vref. Just remember to put power back in on level off, or the plane will quickly stop flying.This was a dive bomb into the field, ATC held us high to let an F35 underfly us on the way to Hill AFB then cleared us to land.

 

[Palmpilot]

...If you're high on the approach the trick is to slow down first and then go down..

I’ve never flown an airplane that lets you go down and slow down...

In the piston spam cans that I fly, the trick is to slow down to flap-extension speed before beginning the descent.

Referencing the thread where I was whining about being held at 6500 on a VFR approach into the SFO area, I wish I had slowed down as soon as I got that instruction. I suspect it would have made things easier for everyone concerned.

 

[EdFred]

Nose up slips baby!

 

[Velocity173]

I always figured they had the lowest seniority controller(s) walk the runway before each shift and police any TOD they found...

They actually do that at some bases in the Marines. Navy probably does it as well. Every morning before field opening, anyone not on position (junior controllers) walk the ramp with the other shops. Obviously it’s for FOD (not TOD) and they don’t go on the runway.

 

[Skinnybird]

They actually do that at some bases in the Marines. Navy probably does it as well. Every morning before field opening, anyone not on position (junior controllers) walk the ramp with the other shops. Obviously it’s for FOD (not TOD) and they don’t go on the runway.

Army did the same, all the E-1s to E-4s regardless of MOS. And we walked the runways too.