IFR - FAQ

Can you dip below DA or MDA?

DA: can dip below, you need to make a decision at DA, but do not have to level off.
MDA: cannot dip below, must be level off before reaching MDA.

Does MEA guarantee comm coverage?

MEA does not guarantee comm, only nav.

Do you need to report when you are at a compulsory reporting fix?

Only when no radar contact.

What's the standard IFR takeoff minimum?

Part 91: no standard takeoff minimum
Part 121/135: 1 sm visibility for 1 or 2 engines

What's the standard IFR departure?

35 AGL at the end of the runway
fly runway heading to 400' AGL
default climb >=200' per NM if not specified

Can you fly in the cloud without ifr clearance?

Yes in class G

What if the aircraft is not equipped with an alternate static source?

Break the glass face of the VSI, allowing the altimeter and airspeed indicator to function.

What to do if air induction is blocked?

carbureted aircraft engines: carbureted heat control is the alternate air induction control. If air induction is blocked, open carberator heat, air will bypass the filter
fuel injected: e.g. C172, if air filter is blocked, a spring-loaded flap that automatically opens; no pilot control.

How many AHRS/ADS do we have?

Depends on the aircraft. C172 has one each, Cirrus have two.

When is compass accurate?

During unaccelerated flight.

What are compass errors?

magnetic dip - accelerate(ANDS)/turning error(UNOS, howto make a turn, 90 to 360, stop turning at around 330; 90 to 180, overshoot, turn pass 180 by 30, to 210 then roll out), small near equator,
Deviation - installation error, compass corection card; G1000, heading indicator also need deviation, software params; 6-pax heading indicator does not have correction, must match compass with correction
Variation

What if pitot tube is blocked?

if both ram air input and the drain hole are blocked, the airspeed indicator may respond as an altimeter.
if ram air input is blocked but the drain hole is not, airspeed will show 0.

What's the relationship between temperature and pressure?

Lower temperature, lower pressure.

When the ambient (at altitude) temperature is colder than standard => lower pressure => higher altimeter reading => the aircraft's true altitude is lower than the indicated barometric altitude.

The molecules are moving slower because it’s colder, which allows them to get closer together, but also means less collisions with the walls of its container which means lower pressure.

"high to low, look out below": if fly from high pressure to low pressure, or high temperature to low temperature, actual altitude will be lower than indicated.

Another way to help remember this is that some approach plate may have the snowflake, which indicates a cold temperature altitude correction will be required on an approach, otherwise you may risk flying too low.

How often are the databases updated?

NavData: every 28 days
Obstacle databases can be updated every 56 days

What if the GPS database is expired?

What you generally CAN do:

En Route and Terminal Navigation (with verification): You can typically use an expired GPS database for IFR en route and terminal navigation, provided that you verify the accuracy of the points and routes to be used against current, approved paper or electronic charts. This means you cannot solely rely on the expired database for your navigation. You must cross-reference the information to ensure its validity.
Situational Awareness: An expired database can still be used for situational awareness, providing a visual representation of your aircraft's position relative to airspace, terrain, and charted fixes. However, this should not be considered primary IFR navigation.
Substitution for ADF or DME (with a current database required for the substitution itself): While an IFR-certified GPS can often substitute for ADF or DME, the regulations regarding this substitution generally require the GPS database to be current for the purpose of the substitution. Therefore, using an expired database might preclude you from legally substituting your GPS for ADF or DME requirements on a procedure.

What you generally CAN'T do:

Fly an IFR Approach: You cannot legally fly an IFR approach procedure (such as an RNAV or GPS approach) using an expired GPS database. Instrument approach procedures are subject to frequent changes (on 28-day AIRAC cycles), and using outdated information could lead to navigating incorrectly, missing critical altitude or waypoint constraints, or using outdated navigation facility information, all of which pose significant safety risks.
Use the Expired Database as the Sole Source of Navigation for any IFR Segment: While en route and terminal use with verification is permitted, you cannot rely only on the expired database for any phase of IFR flight. You must have current charts and actively use them to confirm the information presented by the GPS.
Legally Substitute GPS for ADF or DME if the Substitution Requires a Current Database: As mentioned above, the regulations governing GPS substitution for other navigation aids often mandate a current database for the substitution to be legal.
Conduct an IFR Checkride: For FAA practical tests for instrument ratings, the GPS equipment used for the test is typically required to have a current database.

What is "full-scale deflection"?

flying inbound (ENROUTE) 2 nm (each side)
within 30 miles from the airport (TERM) 1nm
starting from final approach fix: 0.3 nm
if LPV: 0.3nm down to 350 ft

ILS 350 ft runway threshold, a full-scale deflection on the CDI corresponds to an angular displacement of approximately 2.5 degrees from the centerline on either side. This means that if the needle is deflected fully to one side, the aircraft is about 2.5 degrees off the intended course.

Angular sensitivity constant: a full-scale deflection on the CDI corresponds to an angular displacement of approximately 2.5 degrees from the centerline on either side.

VOR: constant, Each dot on either side of the center of the CDI represents approximately 2 degrees of deviation from the selected radial. Full-scale deflection of the CDI needle to either side indicates that the aircraft is 10 degrees or more off the selected radial.

What is TERPS?

TERPS stands for the United States Standard for Terminal Instrument Procedures, and it's a set of rules used to design and evaluate Instrument Flight Rules (IFR) procedures for airports in the US.

The ICAO equivalent of the TERPS is PANS-OPS (Procedures for Air Navigation Services - Aircraft Operations). PANS-OPS is the international standard for designing instrument procedures.

For missed approach, can you dip below DA?

Yes, you need to make a decision at DA (not leveling off at DA), if you decide to go missed, you may temporarily dip below DA.

For missed approach, can you dip below MDA?

No, you need to level off at MDA.

What's the difference between "Load" and "Activate" in G1000?

Load: Imports a flight plan or procedure into the G1000, making it available but not actively navigating towards it.
Activate: Commands the G1000 to immediately begin navigating according to the selected flight plan, procedure, or leg.

"Load" does not activate any leg in the approach. This is important because if you just load the approach without activting the leg, if you go missed, it will not automatically sequence you for the published missed procedure.

What are the inputs of AHRS?

Accelerometers: measure linear acceleration along the three axes.
Magnetometers: measure the strength and direction of the surrounding magnetic field, including the Earth's magnetic field. Magnetometer data is used to determine heading relative to magnetic North.

What's the difference between spin and spiral?

spin: the rotation axis is inside the plane.
spiral: the rotation axis is outside of the plane.

What's the difference between green and blue airports?

Both have published IFR approaches. Blue airports have approaches that start from high-altitude.

When is 600-2/800-2 required?

At ETA. This is different from the 1-2-3 rule. I.e. for destination the weather requirement is from 1 hour before to 1 hour after; for alternate the weather is at the ETA.

Does landing minimum depend on ceiling?

No. Ceiling is required only for planning; when flying, only visibility matters.

For example, when flying in fog, there's no ceiling, as long as you have enough visibility you can land. When listening to ATIS, pay attention to visibility.

What are the components of ILS?

Guidance: localizer, glide slope
Range: marker beacons, DME
Visual: approach lights, touchdown lights, runway lights.