Speed limits?

According to the knee board, I should be doing 477 knots (GS).

If I try to go over 320 (IAS) I get an over speed warning. (737).

Is that normal?

According to the knee board, I should be doing 477 knots (GS).

If I try to go over 320 (IAS) I get an over speed warning. (737).

Is that normal?

Read up in IAS v TAS. Then read up on IAS v altitude.

There's your answer.

According to the knee board, I should be doing 477 knots (GS).

If I try to go over 320 (IAS) I get an over speed warning. (737).

Is that normal?

Try setting to TAS. true airspeed.

is that over 10000 feet ?

Remember that the higher you go the thinner the air gets, so your IAS may be 250 kts, just for an example, but your GS is 397. Also, the higher you get, the lower your Vne, again, the thinner the air. Watch you airspeed indicator. As you go higher and higher, the red-line on it will get lower and lower. I don't know that a 737 can go high enough, but the SR-71, for example, flies at what's called "The Coffin Corner", or the altitude and conditions (Temperature, air pressure, humidity, etc) at which Vne and stall speed are very very close together. The ground speed may be 1800MPH or more, but the indicated airspeed is down to, say, 200 kts, or whatever stall is for that bird. They fly a very delicate balancing act, and I wager your plane may be experiencing a similar effect, even if not in the Coffin Corner.

You can slow down, as long as you stay above stall, to stay below Vne, or you can go lower and get into thicker air. Even a thousand feet can make a large difference.

It's all a matter oc not comparing apple and oranges. IAS, TAS and GS are all different animals, and can't be utilized in the same way. To fly the plane safely, that is above stall, but below Vne, you need to watch IAS. It's the true indication of what the air and the plane "mean" to each other. If you monitor GS or TAS, you will go over Vne constantly.

Does all this help a little? Make it about as clear as good San Fransisco fog?

Pat☺

...so your IAS may be 250 kts, just for an example, but your GS is 397.

TAS is more relevant. GS means something in this sense only if winds are dead calm, since it would be the same as TAS only under those conditions.

You might note that all aircraft have something like a "coffin corner," but many with fewer potential problems, if it's reached, than an aircraft such as the SR71. As an aircraft climbs (say a C-172), its max achievable indicated speed (IAS) drops, as you've noted, until it merges with stall speed. On a C-172 this might be 14,000-15,000 or so, at max gross weight. So a little higher is the absolute ceiling, and as you approach this it's in the "coffin corner." But we don't normally use the term with light aircraft.

Watch you airspeed indicator. As you go higher and higher, the red-line on it will get lower and lower.

On many computerized indicators that may be, but not on the typical older round, or analog dials (I despise the term "steam gauges," since steam was never involved) - the red line is painted on the dial.

To OP (farrout):

According to the knee board, I should be doing 477 knots (GS).

If I try to go over 320 (IAS) I get an over speed warning. (737).

Is that normal?

That kneeboard should be referencing TAS (True, or actual, AirSpeed), not Ground Speed. But as Pat says, the lower IAS is normal, due to the thinner air: IAS is just a reading of air pressure into the pitot tube, but calibrated in terms of airspeed (at sea level) instead of inches of mercury or pascals. So thinner air provides a lower reading at the same actual speed through the air (not over the ground).

In a jet such as the 737, you need to be switching to mach speed once the climb IAS

merges with the planned mach speed. If you try to fly the climb IAS past that point, you

will exceed the usual mach speed, and start approaching supersonic, and thus will be

going over speed, which will cause mayhem and eventual destruction of the airframe. :(

If flying VNAV, the change is automatic, but if you don't have an FMC, which the default

Boeing's do not have, you will have to switch manually.

Say you climb out at 300 knots IAS once you pass the 10,000 250 knot limit..

You will climb at 300 until the point you merge with the planned mach speed, which in

the 737 is usually in the mach .78-.79 range.. Will vary due to the cost index, etc..

So if at 300 IAS, you will merge with mach .78 around FL310 or so, plus or minus.

At the point you see the mach .78, or whatever, then you will hold that mach speed,

and the IAS will gradually roll back the higher you climb. If you cruise at say FL370,

the IAS will be well under 300 knots.. More like 250-260 or so, plus or minus..

When you descend, do the same thing backwards.. Descend at the planned mach

speed, until you merge with the planned descent IAS speed, and then convert to IAS,

which often will be about the same as the climb speed, but again will vary to the type of

descent, cost index, etc.. You can descend at the same 300 knots if you want, which

is fine.. Then back to 250 knots when you descend below 10,000 ft.

The TAS and GS are used more for timing arrivals to way points and such, calculating

tail or head winds and such than actually flying the plane, which are done by the IAS

and mach speeds.

Remember that the higher you go the thinner the air gets, so your IAS may be 250 kts, just for an example, but your GS is 397. Also, the higher you get, the lower your Vne, again, the thinner the air. Watch you airspeed indicator. As you go higher and higher, the red-line on it will get lower and lower. I don't know that a 737 can go high enough, but the SR-71, for example, flies at what's called "The Coffin Corner", or the altitude and conditions (Temperature, air pressure, humidity, etc) at which Vne and stall speed are very very close together. The ground speed may be 1800MPH or more, but the indicated airspeed is down to, say, 200 kts, or whatever stall is for that bird. They fly a very delicate balancing act, and I wager your plane may be experiencing a similar effect, even if not in the Coffin Corner.

You can slow down, as long as you stay above stall, to stay below Vne, or you can go lower and get into thicker air. Even a thousand feet can make a large difference.

It's all a matter oc not comparing apple and oranges. IAS, TAS and GS are all different animals, and can't be utilized in the same way. To fly the plane safely, that is above stall, but below Vne, you need to watch IAS. It's the true indication of what the air and the plane "mean" to each other. If you monitor GS or TAS, you will go over Vne constantly.

Does all this help a little? Make it about as clear as good San Fransisco fog?

Pat☺

Great way of helping someone understand this (Like me)!! I have not flown an aircraft since 1981 but I always wondered about this bizarre side of natural forces at work. My thought was always about the pilots of a 747 cruising at 44,000 MLS. I imagine they would not be reading Ernest Gann's Book "Fate is The Hunter." I never made it over 10,000MSL except in FSX. If you get sloppy at high altitude, the plane stalls in FSX. Fate is The Hunter is a good book about the flying adventures of Gann in the early days of commercial flying when the physics of flying were still being learned. The movie is not about the book though.

J Redd