Gauges RL vs Simulator... and... flight rule tolerances?

[yallu]

Just a couple of questions I have been interested in but never really gotten into asking:

1) How are gauges RL vs Sim? Some of the RL videos show gauges much more "nervous" than FSX. Are they? How about, for example, VSI, is it too accurate and too responsive in FSX compared to RL? Same goes for other instruments like IAS?

2) What are the tolerances in staying on route, staying on alt  etc. (N nm, N feet)? Same tolerances apply for DME arcs? Or in other words, are there exceptions/more strict rules depending on current flight situation? Are these international or are there country specific rules?

[Ryan Mason]

I can only tell you from a helicopter perspective, but my HSI, airspeed and VSI all twitch a little bit dependant on what stage I am at (spooling up/forward flight/hover) the RPM needle usually rattles until in forward flight.  Also the VSI and altitude take about 1/2 to 1 full second to respond during descent.  Just my 2c to your question.

[Patrick Cox]

I was a passenger on a charter flight from Bathurst to Walgett in a Piper Commanche last Sunday and the gauges were rock steady.

On Thursday I returned to Bathurst on a Cessna 310 and likewise all gauges were rock steady.

In flightsim I find that the VSI in the default aircraft and a few other aircraft is very twitchy but try not to take a lot of notice of it otherwise you would be chasing it all over the place. An exception to this is the default Piper J-3 Cub.

Where I can, if it is fitted, I use the autopilot once I have reached my chosen altitude like most pilots do in RL.

Cheers

Pat

[John Bosch]

I found that in a C150 the gauges wouldn't shudder as such, but weren't particularly steady either. They are steady enough that you can fly VFR and practise IFR, but you wouldn't want to fly IFR for long! In the C172 the gauges are rock steady and move very smoothly.

The main issue with the VSI is that it is a delayed instument. It takes time for the air pressures within it to stabilise. It works by having a bladder with one side open to the actual outside air pressure while the other side is only open to the outside air via a very small hole. The second side takes time to adjust to the outside air pressure. So it is always just a little bit behind your actualy rate of climb. Chasing it is not a good idea because it is actually chasing you! 

As for tolerances, for the GFPT it is meant to be staying within 100' of your assigned altitude. Heading is a little different and depends on what you are doing. In level flight I'm not sure there is a set limit but I reckon the instructor would be concerned if you were more than a few degrees off for any reasonable length of time. You should be able to recover from a stall with the nose within 10° of where it started, and from a steep turn within the same.

Really, staying within 100' and a few degrees isn't that hard in real life. I actually find it harder in the sim it is harder because the aircraft feel more "floaty" .... or something. I feel the same within racing sims too ... real life driving is easier.

[Maurice_King]

1) How are gauges RL vs Sim? Some of the RL videos show gauges much more "nervous" than FSX. Are they? How about, for example, VSI, is it too accurate and too responsive in FSX compared to RL? Same goes for other instruments like IAS?

In some Aircraft they can be somewhat hesitant but this may be because the instrument is old perhaps and should be services or replaced. The VSI in some planes can be sensitive but in FSX IMHO is is pretty close to the real deal - remember this instrument will react to the slightest amount of climb or decent faster than the any altimeter will, a TE Electric Vario-meter in many Sail Planes for instance will react to climbs as little as 5 ft / min.

Now depending on the mass of the Aircraft ie it's inertia the instruments may appear to be rather sluggish, simply because the aircraft is reacting slowly.  The instruments themselves are identical in operation , the main difference being you don't have a static source and or physical external input to the instruments in the simulator and are confined to the internal constraints of the actual mathematical information available for the XML files and other inner working of how the gauge works in the sim.

The frequency of update relative to many other factors in the flight model, the simulated weather and environment in which your flying will also have an effect on how the instruments perform.

2) What are the tolerances in staying on route, staying on alt  etc. (N nm, N feet)? Same tolerances apply for DME arcs? Or in other words, are there exceptions/more strict rules depending on current flight situation? Are these international or are there country specific rules?

I have heard it said the 100' 10 Kts and 10 Deg are allowable variances. As long as there are corrections made.

It is a hard question to answer fully because it would depend on the region in the world your flying whether it's VFR or IFR rules that you are flying too.

To me if I am more than 3 Nm either side of my intended route at the mid point say or make an excursion more than 150 Ft above or below my planned cruising alt I get VERY annoyed with myself.

In many ways VFR is harder than IFR because you MUST maintain a good Lookout, radio listening and good navigational skills making mandatory Broadcasts when necessary and always be aware of where you are.

There are many flying the VATSIM network including my self that run an INI file containing ALL the geographically correct CTAF and MBZ areas and we make the appropriate calls as well as unicom.

IFR can be a case of watching your instruments to maintain your speed direction and altitude etc and letting the various ATC centre's keep an eye on what your up to and other aircrafts location in relation to you (within reason that is) A good pilot will have his head on a swivel at all times anyway.

Some Aviation rules FSX wouldn't know about if they jumped up and bit it on the arse. The main reason being regional FSX does a great job at replication flight in many ways but to be able to replicate various VFR and IFR rules and local anomalies would be neigh on impossible.

I hope this has helped explain your questions.

[Martin Henare]

You can add RVSM to this too.

Reduced Vertical Separation Minima, is the requirement for any aircraft operating above FL280. The requirement allows a minimun vertical separation of 1000ft, where piror to RVSM above FL280 it was 2000ft.

Due to the accuracy of moden aircraft systems, RVSM was introduced to allow more aircraft to operate in a given airspace, aswell as being able to fly at more favorable altitudes for speed, fuel ecnonmy etc etc.

The tolerance of an RVSM aircraft is that it must be able to maintain its altitude within +-65ft in level flight. It must have two independent altimeter sources, a minimum of one Altitude Control system (Autopilot), an altutude alert system warning of a +-200ft discrepancy.

If an aircraft is not certified as RVSM compliant it is not allowed to operate above FL280 unless a special exeption is granted. But can operate above FL410. (a bit high for your average cessna)

The small irony of the accuracy of modern avionics is that in the case of the GOL/Legacy collision over Brazil a few years ago it is likely the collided because they were flying at almost exactly the same altitude. The Legacy was probably about 5ft lower and flying 2/3rds the wingspan to the left of the Boeing. Its winglet severed the wing of the 737 cutting of about 6m off the wing sending the 737 into fatal spin. the Legacy recovered with just a damaged winglet and some slight damage to its tail. For those who dont know the Legacy Crew had accidently turned off their TCAS, and they and ATC had forgetten to change their altitude at a previous reporting point.

The old days they would probably have passed with in a few hundred feet and not even been aware of each other. The Legacy crew never saw the 737, just a flash of a shadow, they took a while before they even realised they hit something after the initial impact.

[DavidP]

From the Australian AIP (ref ENR 1.1-36 19.6.2):

Tracking tolerances in CTA:

VOR/LOC - half scale deflection

NDB +/- 5 degrees

DME +/- 2 nm

RNAV +/- 2 nm

Visual up to 1 nm from cleared track

David

[yallu]

Great replies, thank you.

[tim_A]

I think also the tolerances get smaller if you go for a CPL: - +/- 50ft and 5 degrees on height & heading, quarter-scale defection on the VOR etc, also nosewheel must be on the runway centre line.

[DavidP]

I think also the tolerances get smaller if you go for a CPL: - +/- 50ft and 5 degrees on height & heading, quarter-scale defection on the VOR etc, also nosewheel must be on the runway centre line.

I don't think so. For an IFR rating, it is +/- 100 feet (0 at minima - i.e. don't bust the minima), speed is +/- 10kt and heading is 5 degrees (see CIR Test form from CASA web site). The tolerances I quoted in my post above are the tolerances that also apply for an IFR rating.

There is no known requirement for a nose on centreline - more like a safe landing would be the requirement.

David