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Aviation => Pilot/Controller Forum => Topic started by: stonemin on September 30, 2014, 10:06:46 PM

Title: VFR, IFR AND IAP...
Post by: stonemin on September 30, 2014, 10:06:46 PM
Hello, i'm not native english speaker and i've studied ATC to be air traffic controller.

and i confuse the exact meaning between vfr and ifr.

i believe that vfr means Operation under only VMC and pilot must see and avoid any traffic or obstacle and ifr means Operation under only instrument and can operate in not olny VMC but also IMC.

but my thinks got confused when i study Visuall apprach.

Manual book says Visual approach is not IAP but still on IFR. but i think Visual Approach use the pilot's eye not instrument. so i think Visuall Approach is not IFR but VFR.

Does IFR mean that pilot only use instrument not visual? Is it VFR if pilot use he's eye to fly or land? Can IFR plane use pilot's eye? If VFR Pliot use navigation to fly, is it ifr not vfr?

and In the IAP, pilot must decide whether descend  or not at MDA/DH. Does it mean in the approach after MDA/DH, the pilot use their eye's not instrument? If it is yes, Is it VFR?

Title: Re: VFR, IFR AND IAP...
Post by: martyj19 on September 30, 2014, 10:41:06 PM
Most of the confusion you are having is between VFR and VMC and between IFR and IMC.

Under Visual Flight Rules, the pilot is responsible for separation from other traffic.  This is accomplished by requiring the pilot to be in Visual Meteorological Conditions at all times.  This means three miles visibility and specified clearance from clouds.  The cloud clearance requirements are to make sure that an IFR aircraft doesn't emerge from a cloud so close that the VFR aircraft can't see and avoid it in time.  Under VFR, the pilot need not be in contact with ATC unless nearing or inside control zones such as Class B, C, D airspace.  In dark night VFR, the pilot will be using the instruments heavily since there is no visible horizon to refer to.  At least in the US, a VFR pilot need not file a flight plan (in most cases) and can use any means of navigation, including reference to landmarks on the ground, VOR/NDB radio navigation aids, or GPS.

Under Instrument Flight Rules, the controller is responsible for separation from other traffic.  Because of this responsibility, under IFR, the pilot is always in contact with ATC.  This is true whether or not the flight is in VMC or IMC.  The controller will use radar or other techniques to keep track of separation and issue clearances to ensure that traffic remains separated and gets to where it is going.  When an IFR flight is in VMC, the pilot should be seeing and avoiding also.  The pilot will be on instruments in IMC, since there is no other way to keep the aircraft from an upset.  They may or may not be on instruments in VMC.  The pilot must file an IFR flight plan and be cleared for a route by ATC and may be re-cleared as conditions develop over the course of the flight.

A visual approach is not an Instrument Approach Procedure.  It can be given when the pilot is in VMC and reports the airport and the traffic they are following in sight.  The pilot will fly using visual cues from being cleared for the approach all the way to touchdown, but they are still under IFR.

On an instrument approach, the procedure itself is responsible for terrain avoidance above Minimum Descent Altitude/Decision Height.  If flown according to the charted approach with the appropriate altimeter setting, the aircraft is guaranteed obstacle clearance down to MDA/DH.  If flown with controller issued vectors, the controller remains responsible for terrain avoidance and will do this by using Minimum Vectoring Altitudes.    When you get to MDA/DH, you must have the "runway environment in sight" (one of a dozen or so things are acceptable) and from there you would complete the landing using visual cues, and once again you are still under IFR.  If you don't have the runway, or lose it before touchdown, you must initiate a missed approach and fly the published missed procedure until ATC issues a different clearance.

There are many little exception cases in what I've outlined.

I hope my English is understandable and please ask further questions if you want.

If possible, I encourage any ATC student to take a flight and experience these things from the pilot perspective.
Title: Re: VFR, IFR AND IAP...
Post by: stonemin on October 01, 2014, 12:34:00 AM
Thank for your answer
but i still have some doubt about IFR and VFR.

Is it correct that IFR can have visual flight(depending pilot's eye) not instrument in VMC? If yes, Does IFR include VFR?

and why should IFR flight have clearance(including route... etc)? i mean, Why don't IFR flight fly where they want to go like VFR? I know VFR flight can fly everywhere they want to go as maintaining VMC.
so Is it possible IFR flight fly everywhere they want to go(not planned route) and when they encounter IMC, they use instrument(IFR) and just keep flying(in the IMC)?

why IFR flight must get clearance(including route), and fly as planned route?

and I know there's vfr altitude(like 3,500ft, 5,500ft), and i have some question about it.
I believe VFR flight are free in flying, and they just see and avoid some obstacle. But when they fly as vfr altitude and encounter cloud, i think they must keep VMC so they should descend or climb to avoid cloud. it means they have free in choosing altitude. So i think the vfr altitude disturbs VFR flight to maintain VMC. Why is there vfr altitude which restrict them maintaining VMC ?

I know this is fundamental question.. but i can't find my answer by searching in google..

I hope you make answer about my question, thanks..
Title: Re: VFR, IFR AND IAP...
Post by: N/A on October 01, 2014, 12:56:31 AM
Title: Re: VFR, IFR AND IAP...
Post by: martyj19 on October 01, 2014, 12:58:00 AM
Under IFR, you can fly visually rather than on instruments if you are in VMC.  But remember that large aircraft usually engage the autopilot so it is flying the cleared route very precisely without any eyes involved.  No, IFR does not include VFR.  You are on one set of rules or the other at any one moment in time.

It does happen that a VFR flight starts to get into IMC or needs to get down through clouds and then requests an IFR clearance.  Assuming that the pilot and aircraft are IFR rated and equipped it could be granted.  We call that a "pop-up clearance" or an "air file".  Once accepted by ATC the flight is then under IFR.  More than likely you wouldn't then transition back to VFR, though you could.  This is called "cancelling IFR".  Also, scheduled air service is routinely filed IFR and end of discussion no matter what the weather.

There are two main reasons why IFR flight has a cleared route.  One is that the controller will know what to expect from the aircraft.  It will fly the cleared route.  This is essential to the controller's job of maintaining separation.  Two is that in the event of radio communications failure, the aircraft will fly the cleared route.  When that happens, the controller will move other aircraft away from the radio-failure aircraft.

When you are VFR and on a VFR altitude like 3500 you will maintain your altitude and fly around the cloud or you will climb or descend to another VFR altitude to avoid the cloud.  You are not free to choose your altitude.  See

Title: Re: VFR, IFR AND IAP...
Post by: stonemin on October 01, 2014, 03:26:54 AM
really thank you..

actually, i understood that IFR means pilot must depend on the instrument not visual so far as. so i wonder why visual approach is IFR. because visual approach needs VMC and pilot must see the airport or the preceding aircraft.

but according to your answer, IFR means pilot mostly depends on the instrument, and also depends on their eye. is it correct?

if yes, i have misunderstood the meaning of IFR. Thanks for your answer. it really help me to understand about IFR and VFR.
Title: Re: VFR, IFR AND IAP...
Post by: martyj19 on October 01, 2014, 10:07:06 AM
Once more, whether you are on instruments or not has nothing to do with whether you are under IFR or VFR.  You have misunderstood that part.

You need to be on instruments any time you do not have sufficient vision outside the aircraft to keep it stable and upright.  You can only legally go below VFR minimums when you are IFR.  But you will fly visually when you are on a visual approach or the part of an instrument approach below minimums.
Title: Re: VFR, IFR AND IAP...
Post by: N/A on October 01, 2014, 11:35:10 AM