Chop and drop

Richard

Richard

Final Approach
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Ack...city life
I'm inbound from the west at 2,000 (TPA) just about to enter downwind. ATC calls a Cessna C-172, 2,700' 3 nm, 2 o'clock. I report not in sight. *sigh*

Not more than 30 seconds later I'm mid-field left traffic for 26L and I look below me to see the Cessna at what must've been CTL min alt.

Day-am, I hate this!

I was monitoring TWR for the last 10 minutes and I hadn't heard anything from the Cessna until he acknowledged cleared to land 26L. Neither the Cessna nor ATC advised of practice IFR approach.

Now having looked at the VOR-A plate I see why the rapid change in altitude for the Cessna.

http://204.108.4.16/d-tpp/0712/05218VGA.PDF

EDIT: And I didn't expect a Category A aircraft to be making 140 KIAS after GOLDI. How else to explain the rapid change of location and altitude?
 
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Wow. Wonder if the tower meant 1700'....

These days, having the TIS on the Garmin offers a LOT of spatial information that I don't always get from the controller.

Any chance that you have the tail number to look up on FlightAware?
 
SkyHog said:
Moi Aussi, but only at the lower elevations.
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Well. It would be rather tough to maintain 140 KTAS in level flight at any altitude in a C172. But once you take the "level flight" out of equation 140 KTAS and greater can be achieved. Add some wind and 140 knots GS in level flight is a piece of cake.

The thing is--yeah--your indicated airspeed is lower. But the difference in KTAS at 1,200 feet and some of the higher altitudes (up to around 8,000) is only a couple of knots.
 
jesse said:
The thing is--yeah--your indicated airspeed is lower. But the difference in KTAS at 1,200 feet and some of the higher altitudes (up to around 8,000) is only a couple of knots.
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At 1200 MSL, OK, but at 8000 MSL the difference for a 172-class aircraft is around 13 knots on a standard day.
 
Ron Levy said:
At 1200 MSL, OK, but at 8000 MSL the difference for a 172-class aircraft is around 13 knots on a standard day.
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Uh. Okay. I'm talking cruise speeds here.

8,000 ft, standard temperature, 70% power, 120 KTAS, 8.0 GPH
2,000 ft, standard temperature, 75% power, 116 KTAS 8.4 GPH

And for the "but it's colder up there!" argument
8,000 ft, 20C below standard, 76% power, 120 KTAS, 8.6 GPH

I flew the DA-20 back from 6Y9 at 10,500 feet. The engine still produced enough power to red-line the prop. The true airspeed based on my measurements in flight and the POH was within 5 knots of what I would have had at 1,200 MSL.

In my experience, most normally-aspirated pistons, can get a pretty similar cruise KTAS between the altitudes I fly at (1200 MSL) up to around 8,000 ft. The higher you go, the less fuel. It might vary a couple knots but in the real world with varying winds a couple knots is pretty minimal. It always bothers me how some pilots never go up high because they have it stuck in their head that they'll be so much slower. In reality, if anything, their KTAS will be within a couple of knots up to around 8,000 ft and their fuel burn will be lower.

Yes high density altitude flying requires attention. Yes takeoff performance sucks. Yes landing performance sucks. The way the airplane handles is KIAS. The way your stop watch is going to work is KTAS.
 
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jesse said:
Uh. Okay. I'm talking cruise speeds here.

8,000 ft, standard temperature, 70% power, 120 KTAS, 8.0 GPH
2,000 ft, standard temperature, 75% power, 116 KTAS 8.4 GPH

And for the "but it's colder up there!" argument
8,000 ft, 20C below standard, 76% power, 120 KTAS, 8.6 GPH

I flew the DA-20 back from 6Y9 at 10,500 feet. The engine still produced enough power to red-line the prop. The true airspeed based on my measurements in flight and the POH was within 5 knots of what I would have had at 1,200 MSL.

In my experience, most normally-aspirated pistons, can get a pretty similar cruise KTAS between the altitudes I fly at (1200 MSL) up to around 8,000 ft. The higher you go, the less fuel. It might vary a couple knots but in the real world with varying winds a couple knots is pretty minimal. It always bothers me how some pilots never go up high because they have it stuck in their head that they'll be so much slower. In reality, if anything, their KTAS will be within a couple of knots up to around 8,000 ft and their fuel burn will be lower.

Yes high density altitude flying requires attention. Yes takeoff performance sucks. Yes landing performance sucks. The way the airplane handles is KIAS. The way your stop watch is going to work is KTAS.
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I try not to disagree with you too much, Jesse, because you're usually right, but as someone who flies out of these high elevations, I have to say that you're simply incorrect. You're quoting book numbers that are assuming certain temperature conditions, because I can assure you that diving a 172 towards KAEG, you will never hit 130, and certainly not 140.

In my old Cherokee, the difference in speed was amazing at lower elevations. Takeoff run was much shorter (much much much shorter), and the plane actually performs.
 
SkyHog said:
You're quoting book numbers that are assuming certain temperature conditions, because I can assure you that diving a 172 towards KAEG, you will never hit 130, and certainly not 140.
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I assure you that I can reach 130 knots, 140 knots, and Vne (KIAS, or KTAS), in a Cessna 172 diving towards KAEG. Keep in mind that "towards" KAEG might very well mean over KAEG pointing straight down.

As far as cruise altitude. Almost all my flights are around 8,000 ft. It's smooth and the performance hit is minimal. It gives me the most options in the event of a failure.

Obviously, takeoff performance, and KIAS are going to suffer at altitude.
 
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Gee, this wasn't supposed to be about C-172 performance.

Two scenarios:

  • ATC was in error when he called the Cessna at 2,700. This would mean the 172 was below min alt for that segment (assuming TWR accurately reported the position of the 172). After talking with a local CFI, I understand just inside of GOLDI is typically where APP hands IFR traffic to TWR.
  • ATC was correct about the 172 alt and distance. And within a couple miles the Cessna was blo my alt. This would jibe with as shown on the app plate.
The question is how he got from his last reported position (as reported by TWR) to underneath me in less than a minute. The only thing that makes sense to me is he kept the power in as he pushed over for the descent.

Either the pilot was behind the plane and hadn't configured for the descent profile or he was proficient enough that he flew the app faster than what was expected for that category airplane.
 
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Here's the other question - did ATC specify that it was a C-172, or did they simply say a "Cessna"?
 
One is not required to fly a particular approach profile just because the plane can fly it that slowly. I've flown a class D (barely) in a 172.

The point is, nowhere is it written that just because you can fly the approach as slow as 90 that you must.

~ Christopher
 
jwriteclub said:
One is not required to fly a particular approach profile just because the plane can fly it that slowly. I've flown a class D (barely) in a 172. The point is, nowhere is it written that just because you can fly the approach as slow as 90 that you must.
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Well, there are many good non-regulatory reasons for keeping your instrument approach speed down around 1.5 times Vs in the approach configuration (or the top of the white arc, whichever is lower), but the biggest concern is that whatever speed you do fly, you use the minima for the category in which that speed falls, lest you hit something solid by going outside the protected airspace.
 
Well, there are many good non-regulatory reasons for keeping your instrument approach speed down around 1.5 times Vs in the approach configuration (or the top of the white arc, whichever is lower), but the biggest concern is that whatever speed you do fly, you use the minima for the category in which that speed falls, lest you hit something solid by going outside the protected airspa
Click to expand...

All true, however, it is my experience that in busy airspace, barticularly Bravo, that the controllers may ask you to fly approaches at a much higher speed than you might pick if it were you choice.

It is (to my mind) worthwhile, therefore, to occasionally practice an approach (1 in 10?) at a high speed, so as to be comfortable with this.

~ Christopher
 
Richard said:
On call to advise of traffic, TWR said "Cessna 172".
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Well now, could that have been a Cessna with tail number something like N-XX172 ? Wouldn't that become "Cessna 172", and could that be a twin or even a jet?
 
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If my back of the envolope math holds, there are nearly 1300 N**172 tail numbers for arbitrary **.

Just thinkin' if I ever get a citation X.

;)

~ Christopher
 
jwriteclub said:
If my back of the envolope math holds, there are nearly 1300 N**172 tail numbers for arbitrary **.

Just thinkin' if I ever get a citation X.
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Huh? Wouldn't there be, well... 100?

Remember that you can't have NAB172, only N172AB. So the ** would have to be numbers. Otherwise there would in fact be 1,296 possibilities.

Ironically, there's an N172T in my logbook - and it's a Super Cub. :rofl:
 
Richard did say, "Not more than 30 seconds later I'm mid-field left traffic for 26L and I look below me to see the Cessna at what must've been CTL min alt."

I assume he likely could distinguish a twin or Citation from a C-172, but some of the other fast Cessna models may not be so easy from that distance if he was expecting to see a C-172.
 
jwriteclub said:
All true, however, it is my experience that in busy airspace, barticularly Bravo, that the controllers may ask you to fly approaches at a much higher speed than you might pick if it were you choice.
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True, but no pilot should ever allow a controller to push him/her into doing something silly just to expedite traffic.
It is (to my mind) worthwhile, therefore, to occasionally practice an approach (1 in 10?) at a high speed, so as to be comfortable with this.
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Depends on your definition of "high speed" (there are limits, I should think), but if you do, make sure you're using the right minima.
 
Doing instrument approaches in the Skyhawk, my normal approach constant-speed descent is 90 KIAS. I've had controllers ask me to keep my speed up but I won't try to add more than 10 to 15 knots. It's not my responsibility to benefit an aircraft behind me at the expense of risking an unstable approach.

In normal descents, unless there's a need to come down to Va, I'll be descending under power at a stable rate. If I need to lose altitude quickly then the gear comes down but power will stay in. I like airspeed as much as I like altitude and the latter won't hold on without the former.
 
Richard said:
Sure, but see in my OP I say I had a visual on the Cessna. It was a C-172 alright.
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Considering how they said 172--I'm sure it was. But if they didn't it would be easy to confuse a 182 for a 172 in the air. I struggle enough trying to tell the difference from a distance on the ground.
 
At BFI unless you can keep up with the stream of Jet traffic (~ 120 or more) you can hold for EVER.

~ Christopher
 
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