Why is RVSM necessary?

[FlyBieWire]

Can anyone explain why RVSM is necessary above FL 290. What is so special about those higher altitudes?

 

[srjorion]

Honestly, I'm not 100% sure on the scientific answer, but I'll give it a shot.

The higher you go, the less accurate barometric altimeters are. That's why there used to be a 2,000' split above FL290. Now, with the improved accuracy of Air Data Computers and Auto Pilots with altitude hold capabilities we can reduce the error and thus allow aircraft to fly those unused flight levels.

That's my answer. If anyone has a better answer fire away.

 

[3BCat]

The advent of small jets into the national airspace system has shifted commuter traffic from the upper teens to the upper twenties and higher flight levels. It pays to have more altitudes that are usable because more aircraft are in use. Transatlantic/International traffic is also up, so RVSM makes good sense for these operations, too.

 

[some_dude]

Why is it necessary? So Boeing and Airbus will sell more new airplanes, and so a bunch of avionics manufacturers and shops will make money!

 

[Midnight Flyer]

The advent of small jets into the national airspace system has shifted commuter traffic from the upper teens to the upper twenties and higher flight levels. It pays to have more altitudes that are usable because more aircraft are in use. Transatlantic/International traffic is also up, so RVSM makes good sense for these operations, too.

I agree. Back in the day, commuters didn't even have jets, so all their traffic was in the 20's. Now, some commuters (regionals, whatever) are 100% jet, and they're clogging the system.

 

[2000flyer]

Why is it necessary? So Boeing and Airbus will sell more new airplanes, and so a bunch of avionics manufacturers and shops will make money!

RVSM has nothing to do with who sells what. Its a capacity issue. Allowing reduced separation both vertically and horizontally means more aircraft in a given piece of airspace, plain and simple.

 

[FlyBieWire]

The higher you go, the less accurate barometric altimeters are. That's why there used to be a 2,000' split above FL290.

My question is: Why is this true.

 

[340drvr]

Less air density means the difference between, say, FL350 and FL 360 is not as accurately sensed by regular altimeter equipment, thus the need for higher resolution RVSM stuff.

 

[UndauntedFlyer]

I don’t have a reference for this but I believe the need for RVSM separation standards has to do with the non-linear vertical pressure gradient. As we go up in the atmosphere the pressure lowers at a non-linear rate, starting first with about 1” Hg. Per 1000 feet and then gradually getting less with each 1000 feet of increase in altitude. The altimeter must know about this and convert that change into a readable dial showing 20 foot increments of altitude. At some point in the upper atmosphere as we approach outer space you can see that the amount of pressure change per 1000 feet must be very small and almost impossible to measure on even the most sensitive of pressure instruments. Therefore at some point as we go up in the atmosphere there must be a point where an increasingly accurate pressure sensing system must be used if we are going to be able to provide a true vertical separation of 1000 feet as a standard.

In the past such a system was not available at a reasonable cost so the solution was to simply increase the vertical separation standards to 2000 feet for safety when flying above FL290. But now as there is a need for more available altitudes because of increased air traffic, it was decided to develop better altimeter systems and then go ahead and certify those systems that proved to be more accurate by being more pressure sensitive. Thus we now have RVSM and each aircraft that requests to fly above FL290 must be FAA-certified to do so. Also the crew must be FAA-approved to follow certain procedures when above FL290. The crew procedures help maintain the assigned altitude with greater accuracy. Some of those procedures include such things as use of the autopilot and recording a cross reference to a third altimeter for accuracy.

 

[Lrjtcaptain]

RVSM has nothing to do with who sells what. Its a capacity issue. Allowing reduced separation both vertically and horizontally means more aircraft in a given piece of airspace, plain and simple.

Vertically, absolutly, the NAS was wasting so much sky by the 2000ft rule, especially with the increase of RJ's out there.

As for horizontal....well, find me a center that is running you inside of 5 miles at the same alititude. Negative!

hence. REDUCED VERTICAL

 

[WMUSIGPI]

to allow the FAA and politicians to say they are doing something about air capacity without peeving all the NIMBY's fighting against the real solution to congestion...BUILD MORE RUNWAYS!

 

[Turkey Shoot]

I don't know, it pretty rare to converge with someone 1000 below or on top even in the Northeast. (Sure is cool when you do though) More of the biz jets can get to FL450, well above most of the 121 traffic. I have to believe there was a lobby push that got that going. Going into the busy places it sure doesn't help much because you've still got to have separation for the STAR's.

If they really care, get some more controllers. I have a great amount of respect for those folks in ORD approach that are pushing 20 peices of tin and still make a joke now and then.

But my favorite is on GRD there when you get the "(Insert callsign here), what are you doing!?! Just stop, everybody stop. (Callsign) doesn't know where he is or going!" (Last time I heard that, the call sign was Gateway. Go figure.)

 

[2000flyer]

Vertically, absolutly, the NAS was wasting so much sky by the 2000ft rule, especially with the increase of RJ's out there.

As for horizontal....well, find me a center that is running you inside of 5 miles at the same alititude. Negative!

hence. REDUCED VERTICAL

Well, I didn't mean THAT close!!! However, reduced entrail has evolved in the NOPAC and N. Atlantic. With ADS-B and FANS A/B around the corner you'll see entrail come even closer.

 

[some_dude]

I'm sorry, but I'm not buying it. In the North Atlantic, sure. Central East Pacific, sure. Europe, even.

But the US? Give me a break. RVSM in the US was done because of pressure from the Europeans, and so the FAA could feel like we are not inferior to the French.

RVSM has nothing to do with who sells what. Its a capacity issue. Allowing reduced separation both vertically and horizontally means more aircraft in a given piece of airspace, plain and simple.

 

[UndauntedFlyer]

I am sure the USA could have gotten by for a long time without RVSM but why? It was definitely needed in the Atlantic and Pacific as well as Europe, so why not add it in the USA. It just makes everybody’s life easier except for the guy who is operating a jet on a minimum budget. But if you’re a 135 operator just pass the cost on to the customer as everyone else must do.

I am sure the USA could have gotten by for a long time without RVSM but why? It was definitely needed in the Atlantic and Pacific as well as Europe, so why not add it in the USA. It just makes everybody’s life easier except for the guy who is operating a jet on a minimum budget. But if you’re a 135 operator just pass the cost on to the customer as everyone else must do.

Plus RVSM creates more jobs in building more corp jets because the old ones must be scraped. They're too old and leaky to be upgraded. Have you noticed that corp jet sales are at a new record dollar volume?

That was easy. Hit the "Easy Button."

 

[Lead Sled]

Personally, I was one of those guys who accused the FAA of allowing the tail to wag the dog. Imagine, allowing the Europeans (especially ze French) to tell us what we need to do. After all, don't we have more airplanes parked on the ramp at some of our mid-sized "general-aviation" airports than do have in their entire county?

It still frosts me, but when it comes to flight planning, fuel burn, Flight Level selection, etc. it's sure been nice. I wouldn't want to go back to the way it was. About the only complaint that I have with the current system is the way it's implimented. Why can't we handle the recurrent maintainace, training and certification requirements the way we handle things like transponder/pitot static inspections and the existing PPCs? Having this stuff clogg up the system with LOAs and OPSPECS doesn't make a lot of sense to me.

Now about those TAFs and METARs...

'Sled

 

[tracearabians]

The real reason?? MONEY, MONEY, and more MONEY!!!

Can anyone explain why RVSM is necessary above FL 290. What is so special about those higher altitudes?

 

[UndauntedFlyer]

Now about those TAFs and METARs...

'Sled

You got that right on this subject. I hate them. The old SA and TF were much better. At least the temp was in English and everything was in a logical sequence.

 

[2000flyer]

I'm sorry, but I'm not buying it. In the North Atlantic, sure. Central East Pacific, sure. Europe, even.

But the US? Give me a break. RVSM in the US was done because of pressure from the Europeans, and so the FAA could feel like we are not inferior to the French.

So are you saying let the rest of the world accept a certain standard but we in the U.S. are too good for someone elses idea? It's no wonder with an attitude like that we're frowned upon in parts of the world.

Secondly, the rest of the world accepts the new standard but since we don't we'll be severely limited in where and when we can operate around the globe. Worst yet, those operators who wish to comply will be burden with a much higher cost.

Sometimes change is good and others have a pretty darn good idea. Would you feel better if it were an American idea and the rest of the world had to comply?

Yes, having to jump through all the hoops to comply is a burden and the paperwork over blown.

 

[Check 6]

Here is my cynical viewpoint. I was based in S. Europe from 1999-2006. RVSM was implemented during this time in Europe and forced on everyone by Eurocontrol. The modifications involved for compliance cost hundreds of millions of dollars across Europe.

Not all aircraft are capable of compliance with RVSM, but are capable of FL290 and above. What happened in Europe is that RVSM forced these aircraft below FL290 and thus made it more crowded in the lower altitudes. It is not crowded at all above FL280 over Europe. The dense traffic is in the lower altitudes because of the non-compliant RVSM airframes and because of departures and arrivals.

Then the FAA bureaucrats looking for new projects figured they could bring RVSM to the good old USA. If it is good for the French, it is good for America.

Ask the FAA how many incidents of loss of separation occur above FL280 vs. FL280 and below.

We need more runway capacity! We also need more refineries!

If the FAA/Congress force user fees on us our industry will take a dive. I cost us approximately $650 in Eurocontrol fees to fly from S. Italy to London. The FAA would kill for this kind of cash cow.

Lastly there is no doubt that for 1,000 foot separation RVSM is needed at the higher altitudes. Flying formation in Lear 35's at FL310 over Italy our altimeters (current/calibrated/both 29.92) read 700' difference prior to the RVSM conversion. This is how inaccurate they can be.