An altimeter does not measure height directly. It senses atmospheric pressure and converts that pressure into an altitude indication. When that pressure changes, the setting in the altimeter has to change with it.
 
What Altimeter Setting to use?
Correct for nonstandard pressure by setting the current reported altimeter setting in the Kollsman window.
​The Kollsman window is the small pressure-setting window on a conventional altimeter. Turning the adjustment knob moves the barometric scale and changes the altitude indication.

​Below 18,000 feet MSL, 14 CFR § 91.121 requires using either:

1. The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft. Depending on the operation, that information may come from ATC, ATIS, AWOS, ASOS, or another appropriate reporting station.
2. For aircraft without radios or a means to procure the altimeter setting from an appropriate station, you can set the altimeter using the elevation of the departure airport.

At or above 18,000 feet MSL, use the standard setting of 29.92 inHg.
​
The Club's earlier standard-pressure lesson explains why 29.92 inHg is the standard-atmosphere reference. It is not the correct local setting for ordinary flight below 18,000 feet MSL.

Estimate the Pressure-Setting Error
For a quick estimate, 1.00 inHg of setting error is approximately 1,000 feet of altitude error. Therefore:
0.10 inHg ≈ 100 feet
0.25 inHg ≈ 250 feet
0.50 inHg ≈ 500 feet
 
If the altimeter is set to 29.95 but the current setting is 29.70, the setting is 0.25 inHg too high. The altimeter will indicate approximately 250 feet too high, so the airplane is approximately 250 feet lower than indicated.

For the pressure-setting error alone, use this method:

1. Setting in the window - current setting = pressure difference
2. Pressure difference × 1,000 feet ≈ indicated altitude error
3. Approximate pressure-corrected altitude = indicated altitude - signed error

 
Using this week’s example:

1. 29.95 - 29.70 = +0.25 inHg
2. +0.25 × 1,000 = +250 feet of indicated error
3. If the altimeter indicates 3,000 feet, the pressure-only estimate is approximately 2,750 feet

The positive error means the altimeter is reading high. If the setting in the window were lower than the current pressure, the error would reverse and the airplane would be higher than indicated.
 
This is an approximation for understanding the size and direction of a pressure-setting error. It is not a substitute for setting the altimeter correctly.

​This section is summed up neatly by one of our favorite aviation mnemonics:
“Going from high to low, watch out below!”

Pressure and Temperature Are Different Errors
Adjusting the Kollsman window compensates for nonstandard pressure. It does not compensate for nonstandard temperature.
 
Cold air can place the airplane lower than indicated even when the current pressure setting is in the window. Our nonstandard-temperature lesson explains that separate effect.
 
That distinction matters: the quick pressure calculation estimates one source of error, not every difference between indicated and true altitude.

Make It a Cockpit Habit 
Before takeoff, set the current reported pressure and compare the altimeter indication with the known field elevation. During flight, listen for updated settings and put them in the window promptly.

Standard checklists included with all Club aircraft include an altimeter setting check as part of the Taxi Checklist. Additionally, the Run-Up checklist includes a sanity check to verify that the indicated altitude matches the known field altitude.
 
Club members can also practice reading and adjusting a conventional altimeter with the interactive altimeter simulator on GCAC's Aviation E-Teaching Tools page.
 
Common Mix-Ups

• Treating 29.92 inHg as the normal local setting below 18,000 feet MSL
• Reversing the error direction when pressure falls
• Calculating the difference but leaving the old setting in the window
• Assuming a current pressure setting also corrects for nonstandard temperature

 
In a Nutshell
Set the appropriate current pressure in the Kollsman window. If you need to estimate the consequence of a wrong setting, use approximately 1,000 feet per 1.00 inHg.
 
With 29.95 set instead of 29.70, the altimeter reads approximately 250 feet high, placing the airplane approximately 250 feet lower than indicated. Then remember that temperature, instrument, and installation errors are separate considerations.
 
FAA Sources and References
1.  14 CFR § 91.121, Altimeter settings.
2.  FAA Aeronautical Information Manual, Chapter 7, Section 2, paragraphs 7-2-1 through 7-2-3.
3.  FAA Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 8, pp. 8-3 through 8-6 and Figure 8-2.
4.  FAA Aviation Weather Handbook, FAA-H-8083-28B, Chapter 8, pp. 8-10 through 8-12 and Figure 8-13.

Next Week
Airport Operations - Non-Towered Airport Traffic Pattern
 
What is the recommended entry into a non-towered airport pattern when approaching from the opposite side of the pattern?
 
Arriving from the side opposite the traffic pattern takes more planning than simply aiming for the downwind. Next week, we'll compare the FAA's entry options and look at how altitude, traffic scanning, descent location, and local airport context fit together before the airplane joins the pattern.

A pilot can see one speed on the airspeed indicator, calculate another for flight planning, and read a third from GPS. None of those numbers has to be wrong. They are answering different questions.
 
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🧠 The Answer
 

• Indicated airspeed (IAS): The speed read directly from the airspeed indicator, without correction for atmospheric density, installation error, or instrument error.
• Calibrated airspeed (CAS): IAS corrected for installation and instrument error.
• True airspeed (TAS): CAS corrected for altitude and nonstandard temperature. It is the airplane's speed relative to the air mass in which it is flying.
• Ground speed (GS): TAS adjusted for wind. It is the airplane's actual speed over the ground.

 
The short version is:

• IAS is what the instrument shows.
• CAS corrects the instrument reading.
• TAS describes movement through the air mass.
• GS describes movement over the Earth.

 
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🎛️ From IAS to CAS
 
The airspeed indicator measures the difference between pitot pressure and static pressure. That pressure difference moves the instrument's internal mechanism and produces IAS. Our earlier post on the pitot-static system explains that pressure relationship in more detail.
 
IAS is the cockpit number pilots use most often. Airplane operating speeds and limitations are commonly presented as indicated airspeeds, but always confirm the label and value in the aircraft's approved AFM or POH. Club pilots can move from this general lesson to the N84455 aircraft page and its aircraft-specific checklist and in-flight guide for practical reference material; those Club resources support, but do not replace, the approved aircraft information and placards.
 
The instrument and its installation are not perfectly accurate at every speed and configuration. Correct IAS for those errors, using the aircraft manufacturer's calibration information, and the result is CAS.

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🌡️ From CAS to TAS
 
Correct CAS for altitude and nonstandard temperature, and the result is TAS.
 
As altitude increases, air density normally decreases. The airplane must move faster through less-dense air to create the same pitot-static pressure difference. That is why TAS is normally higher than CAS in cruise at altitude.
 
TAS is especially useful for cruise, navigation, and flight planning because it describes how fast the airplane is moving through the surrounding air mass. Temperature matters here, which is why the Club's standard-temperature lesson is part of the same planning picture.
 
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🌬️ From TAS to Ground Speed
 
Wind moves the air mass over the ground. Add that wind effect to TAS, and the result is GS.
 

• A tailwind increases GS.
• A headwind decreases GS.
• A crosswind changes the airplane's track and can also affect GS along the course.

 
This is why a GPS may show a ground speed that is noticeably different from the IAS on the panel. The instruments are measuring different relationships.

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✈️ Which Speed Should You Use?
 
Each speed has a practical job:

• Fly the airplane with IAS. Use the indicated values specified by the AFM or POH for takeoff, climb, stall awareness, approach, landing, and operating limitations.
• Use CAS as the corrected bridge. It accounts for instrument and installation error and is the starting point for finding TAS.
• Use TAS for cruise and flight planning. It describes the airplane's speed through the air mass and supports navigation calculations.
• Plan time and progress with GS. It determines how quickly the airplane covers distance over the ground and therefore affects estimated time en route and fuel planning.

 
One cockpit can display several speed values at once. The useful question is not simply, Which number is right? It is, Which speed answers the decision I am making?
 
//////////////
⚠️ Common Mix-Ups
 

• IAS is not ground speed. A strong headwind can reduce GS without changing the IAS needed to fly the airplane safely.
• TAS is not automatically what the airspeed indicator shows. TAS requires correction for altitude and temperature unless the aircraft's equipment computes and displays it.
• Wind does not change TAS by itself. Wind changes the motion of the air mass over the ground, which changes GS.
• GPS ground speed does not replace IAS. GS is useful for navigation and timing, but it does not provide the same stall-margin and operating-limit information as IAS.

 
//////////////
✅ The Takeaway
 
Follow the correction path:

• IAS corrected for instrument and installation error becomes CAS.
• CAS corrected for altitude and nonstandard temperature becomes TAS.
• TAS adjusted for wind becomes GS.

 
Use IAS to fly, TAS to understand speed through the air mass, and GS to understand progress over the ground.
 
//////////////
📚 FAA Sources and References
 
1.  FAA Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 8, “Airspeed Indicator,” pp. 8-8 to 8-9 and Figure 8-7; Chapter 16, “Navigation,” p. 16-9 and Figure 16-13.

2.  FAA Private Pilot for Airplane Category Airman Certification Standards, FAA-S-ACS-6C, Area I, Task D, Cross-Country Flight Planning; Area I, Task G, Operation of Systems; Area VI, Task A, Pilotage and Dead Reckoning.
 
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📅 Next Week
 
Weather - Nonstandard Pressure
 
How do you correct an altimeter for nonstandard pressure? How inaccurate is an altimeter that is using an incorrect barometric pressure setting?
 
Next week, we'll look at how a mismatch between local atmospheric pressure and the setting used by an altimeter changes what the instrument shows. Even a modest mismatch can matter when altitude accuracy and obstacle clearance are important, so we'll connect the cockpit indication to the airplane's actual position without relying on guesswork.

An airplane can move in many directions, but every change in attitude comes back to three (3) imaginary lines through its center of gravity. Match each axis with its motion and the controls start making a lot more sense.
 
 
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🧠 The Answer
 
· Lateral axis: Passes through the center of gravity (CG) from wingtip to wingtip. Movement about this axis is pitch.

· Longitudinal axis: Passes through the CG from nose to tail. Movement about this axis is roll.
​
· Vertical axis: Passes through the CG at right angles to the other two axes. Movement about this axis is yaw.
 
The key word is about. Pitch, roll, and yaw describe rotation about an axis, rather than translation along it.

The three axes intersect at the airplane's center of gravity. Pitch occurs about the lateral axis, roll about the longitudinal axis, and yaw about the vertical axis. Source: FAA Pilot's Handbook of Aeronautical Knowledge, Chapter 5, Figure 5-18, p. 5-12.
 
 
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🎮 Match the Motion to the Control
 
In a conventional airplane, each primary flight control is associated with one principal motion:
 
·    Elevator or stabilator controls pitch about the lateral axis.
·    Ailerons control roll about the longitudinal axis.
·    Rudder controls yaw about the vertical axis.
 
That is the clean training answer, but the airplane does not divide flight into isolated channels. A control input can affect more than one motion, and normal maneuvering usually combines them.
 
Roll into a coordinated turn, for example, and you use the ailerons to establish bank, the rudder to manage yaw and coordination, and elevator pressure to control pitch and help maintain altitude. The airplane may be rotating about more than one axis at the same time.
 
 
//////////////
✈️ Why the Center of Gravity Matters
 
All three (3) axes intersect at the center of gravity, making the CG the reference point for pitch, roll, and yaw.
 
CG location also affects aircraft stability and handling. Always use the approved loading information and CG limits for the specific airplane.
 
 
//////////////
⚠️ Common Mix-Ups
 
· Longitudinal axis does not mean pitch. It runs the long way, nose to tail, but the airplane rolls around it.

· Lateral axis does not mean roll. It runs laterally from wingtip to wingtip, but the airplane pitches around it.

· Yaw is not the same as a coordinated turn. Yaw is rotation about the vertical axis; a coordinated turn combines bank, pitch control, and properly managed yaw.
 
 
//////////////
✅ The Takeaway
 
Remember the axis, the motion, and the primary control as a set:
 
·    Lateral axis → pitch → elevator or stabilator
·    Longitudinal axis → roll → ailerons
·    Vertical axis → yaw → rudder
 
Picture the three axes crossing at the CG. Once that picture is clear, the terminology becomes much easier to recall in ground lessons, cockpit discussions, and practical-test preparation.
 
 
//////////////
📚 FAA Sources and References
 
· FAA Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 5, “Axes of an Aircraft,” pp. 5-12 to 5-13 and Figure 5-18; Chapter 6, “Flight Controls,” p. 6-3 and Figures 6-4 and 6-5; Chapter 10, “Balance, Stability, and Center of Gravity,” pp. 10-2 to 10-3.

· FAA Airplane Flying Handbook, FAA-H-8083-3C, Chapter 3, “Basic Flight Maneuvers,” pp. 3-1 to 3-5 and p. 3-25.
 
 
//////////////
📅 Next Week
 
Systems - Airspeed
 
Describe the difference between indicated airspeed, calibrated airspeed, true airspeed, and ground speed.
 
· Indicated airspeed (IAS): The airspeed read directly from the airspeed indicator, without correction for air density, installation error, or instrument error.

· Calibrated airspeed (CAS): IAS corrected for installation and instrument error.

· True airspeed (TAS): CAS corrected for altitude and nonstandard temperature. It is the airplane's speed relative to the air mass in which it is flying.
​
· Ground speed (GS): TAS adjusted for wind. It is the airplane's actual speed over the ground.

​Short answer:

·    Aircraft registration: An initial Certificate of Aircraft Registration expires seven (7) years after the last day of the month in which it was issued. The owner may apply for renewal during the six (6) months before expiration.

·    Standard airworthiness certificate: It has no routine calendar expiration date. Unless sooner surrendered, suspended, revoked, or otherwise terminated by the FAA, it remains effective while the airplane is registered in the United States and its maintenance, preventive maintenance, and alterations are performed in accordance with the applicable regulations.

·    Responsibility: The owner or operator is primarily responsible for maintaining the aircraft in an airworthy condition. For N84455, the registered corporate owner is Green Castle Aero Club. Every current, active Club member is a shareholder-member acting as part of that owner/operator, and the pilot in command still must determine that the aircraft is in condition for safe flight.
 
Those answers sound similar when reduced to a flash card, but they work very differently in the real airplane. One  certificate has an expiration date. The other stays effective only while its conditions continue to be met.
 
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📅 Registration Has a Seven (7)-Year Clock

The registration certificate connects the airplane to its registered owner in the FAA Aircraft Registry. Under 14 CFR § 47.40(a), an initial certificate expires seven (7) years after the last day of its issue month.

For example, if the FAA issues the certificate on August 12, 2026, the seven (7)-year period is measured from August 31, 2026. The owner should use the expiration date printed on the actual certificate and begin the renewal process early.

Under § 47.40(b):
·    Renewal may be requested during the six (6) months preceding the expiration date.

·    The owner submits Aircraft Registration Renewal Application AC Form 8050-1B and the required fee.

·    An expired registration is not merely late paperwork. The airplane may not be operated without an effective registration certificate as required by § 91.203(a)(2).
 
The FAA changed the normal registration period from three (3) years to seven (7) years in 2023. That makes old study notes, old websites, and old habits especially easy to trust by mistake. For the current rule, check the current eCFR and the expiration date on the certificate in the airplane.

N84455's registration certificate is a useful real example. It identifies Green Castle Aero Club as the registered owner, lists the owner type as Corporation, and shows an expiration date of December 31, 2027.

​Because this certificate originated under the earlier three (3)-year system and was affected by the FAA's transition to seven (7) years, use its printed expiration date rather than trying to calculate it from the original 2017 issue date.

​//////////////
✈️ The Standard Airworthiness Certificate Works Differently

A standard airworthiness certificate does not need a seven (7)-year renewal. 14 CFR § 21.181(a) says that, unless it is sooner surrendered, suspended, revoked, or otherwise given a termination date by the FAA, an airworthiness certificate remains effective as long as the aircraft is registered in the United States and the applicable continuing conditions are met.

For a standard airworthiness certificate, § 21.181(a)(1) ties continued effectiveness to maintenance, preventive maintenance, and alterations being performed in accordance with Parts 43 and 91.

That is why “it does not expire” is useful shorthand, but not the whole answer.

A better training statement is:
A standard airworthiness certificate has no routine expiration date, but it remains effective only while the aircraft stays properly registered and the applicable maintenance and alteration requirements continue to be met.

N84455's actual standard airworthiness certificate was issued on October 15, 1969. Its age makes the lesson memorable: unlike the registration certificate, it does not show a routine renewal date.

​Its continued effectiveness depends on the regulatory conditions, including proper U.S. registration and compliant maintenance and alterations.

​//////////////
🔧 Effective Certificate Does Not Automatically Mean Airworthy Today

Here is the distinction pilots need to carry into the preflight:
·    Certificate effectiveness asks whether the airworthiness certificate remains legally effective under § 21.181.

·    Current airworthy condition asks whether the airplane conforms to its approved configuration and is in condition for safe operation now.

·    Operating authority also depends on having the required certificates aboard under § 91.203.
 
An airplane can have its airworthiness certificate displayed and still have a discrepancy that makes it unairworthy for flight.

The paper is not a substitute for the aircraft's actual condition, maintenance status, inspections, Airworthiness Directive compliance, or a sound preflight inspection.

This is also where the responsibilities divide:
·    Owner or operator: Under § 91.403(a), primarily responsible for maintaining the aircraft in an airworthy condition, including compliance with Part 39 Airworthiness Directives.

·    Pilot in command: Under § 91.7(b), responsible for determining whether the aircraft is in condition for safe flight and for discontinuing the flight if unairworthy mechanical, electrical, or structural conditions occur.
 
Club preflight check: Before every flight, Club members should review the aircraft's current status in CrewChief Systems and ensure no open squawk, expired inspection, grounding notice, or unresolved maintenance item prevents operation. That review supports, but does not replace, the required document check, aircraft preflight inspection, or the PIC's § 91.7 determination.

For a Club airplane, good records and maintenance systems support the pilot, but the PIC still has a real decision to make before every flight.
 
//////////////
🏰 At Green Castle, the Owner or Operator Means Us

N84455's registration makes the formal ownership clear: Green Castle Aero Club is the registered corporate owner. But Green Castle is not some distant party that Club members can point to when a maintenance, document, inspection, or airworthiness issue appears.

Every current, active Club member is a shareholder. When we use and care for the Club's aircraft, we are acting as part of Green Castle's owner/operator organization. In practical Club terms:
·    Each member is Green Castle. We do not say, “That's Green Castle's issue,” because the Club's responsibilities belong to the membership carrying out the Club's operations.

·    Each member helps protect compliance. Verify required documents and inspections, use the Club's maintenance and reporting systems, and promptly report discrepancies.

·    Do not fly around a problem. If a document, maintenance status, inspection, or aircraft-condition question is unresolved, stop and obtain the proper answer before operating.

·    The acting PIC retains the § 91.7 decision. Shareholder responsibility does not dilute the pilot in command's duty to determine that the aircraft is in condition for safe flight.
 
The corporate entity is the registered owner. The shareholders are the people who make that responsibility real every day.
 
//////////////
📍 What Must Be in the Airplane?

For the certificates discussed here, § 91.203 requires:
·    An appropriate and current airworthiness certificate in the aircraft.

·    An effective registration certificate in the aircraft.

·    The airworthiness certificate displayed at the cabin or cockpit entrance so it is legible to passengers or crew.
 
The PHAK reinforces the same practical point in Chapter 9: the registration certificate is carried in the aircraft, while the airworthiness certificate must be displayed.

GCAC provides digital reference copies of N84455's documents on the Club website. Those copies are useful for study and planning, but they do not replace the required documents aboard the aircraft.

CrewChief Systems is the Club's electronic source for aircraft status, squawks, airworthiness information, and maintenance recordkeeping. It gives members access to the aircraft's maintenance and operating records, but it does not replace the physical certificate requirements: the airworthiness certificate must be displayed in the aircraft, and the effective U.S. registration certificate must be physically aboard.

At Green Castle, the useful habit is simple: know where the aircraft documents are, check the registration expiration date, verify the airworthiness certificate is properly displayed, and do not confuse either piece of paper with a complete airworthiness determination.
 
//////////////
🎓 Why This Shows Up in Training

This is not trivia tucked into a regulation chapter. The Private Pilot Airplane ACS places aircraft certificates in Area of Operation I, Task B, Airworthiness Requirements.

Applicants may be asked about:
·    PA.I.B.K1a: Location and expiration dates of required aircraft certificates.

·    PA.I.B.K1e: Owner/operator and pilot-in-command responsibilities.

·    PA.I.B.S1: Locating and describing airworthiness and registration information.

·    PA.I.B.S2: Determining whether the airplane is airworthy in a practical scenario.
 
The Commercial Pilot and Flight Instructor Airplane ACS documents cover the same family of knowledge and skills. The practical-test lesson is the same as the real-world lesson: find the documents, understand what keeps them effective, and evaluate the actual airplane.
 
//////////////
⚠️ Common Mix-Ups

·    “Registration lasts forever.” It does not. The normal initial certificate has the seven (7)-year expiration rule in § 47.40.

·    “The airworthiness certificate expires every year.” A standard certificate does not have an annual renewal cycle. Annual and 100-hour inspections are separate maintenance and inspection requirements.

·    “The airworthiness certificate is valid even if registration expires.” § 21.181 ties its effectiveness to U.S. registration. The FAA also states that expired registration makes the airworthiness certification ineffective until registration is restored and the other conditions are met.

·    “The certificate proves the airplane is safe to fly today.” The certificate matters, but the airplane's present condition and compliance still matter. The PIC's § 91.7 determination remains essential.

·    “That's Green Castle's issue.” Green Castle is the registered corporate owner, and active Club members are its shareholders. Each member has a role in carrying out the owner/operator responsibilities and protecting the Club's aircraft and compliance.
 
//////////////
✅ The Takeaway

Remember the difference this way:
·    Registration has a date: normally seven (7) years after the last day of the issue month.

·    A standard airworthiness certificate has continuing conditions: proper U.S. registration plus compliant maintenance, preventive maintenance, and alterations, unless the certificate is otherwise surrendered, suspended, revoked, or terminated.

·    At GCAC, the corporate owner/operator responsibility belongs to Green Castle and is carried out by its shareholders; the acting PIC determines safe-flight condition before operating.
 
Check the documents. Check the dates. Then check the airplane.
 
//////////////
📚 FAA Sources and References

·    14 CFR § 47.40, Registration expiration and renewal
·    14 CFR § 21.181, Duration
·    14 CFR § 91.203, Civil aircraft: Certifications required
·    14 CFR § 91.7, Civil aircraft airworthiness
·    14 CFR § 91.403, General
·    FAA Aircraft Registration
·    FAA *Pilot's Handbook of Aeronautical Knowledge*, Chapter 9, Flight Manuals and Other Documents
·    FAA Private Pilot for Airplane Category ACS, FAA-S-ACS-6C
·    FAA Commercial Pilot for Airplane Category ACS, FAA-S-ACS-7B
·    FAA Flight Instructor for Airplane Category ACS, FAA-S-ACS-25
 
GCAC aircraft references:

·    N84455 Airworthiness Documents
·    N84455 Certificate of Aircraft Registration
·    N84455 Standard Airworthiness Certificate
 
Current eCFR wording was checked August 5, 2026. The local PHAK addendum dated October 20, 2025 was also checked; its Chapter 9 change concerns special airworthiness certificate classifications and does not change the standard-certificate duration discussed here.
 
//////////////
🔭 Next Week

Plane & Pilot - Axes of Movement

What are the three (3) axes of movement in an airplane?

·    Lateral axis: Passes through the center of gravity parallel to a line from wingtip to wingtip. Movement about this axis is pitch.

·    Longitudinal axis: Passes through the center of gravity parallel to a line from nose to tail. Movement about this axis is roll.

·    Vertical axis: Passes through the center of gravity at right angles to the other two (2) axes. Movement about this axis is yaw.

Here's the short answer:
 
·   VOR: A very high frequency omnidirectional range facility that provides magnetic directional guidance using 360 radials extending from the station.

·   VOR/DME: A collocated VOR and distance measuring equipment facility, providing directional guidance plus distance.

·   TACAN: A military tactical air navigation system that provides bearing and distance to TACAN-equipped aircraft.

·   VORTAC: An integrated VOR and TACAN facility. Civilian aircraft can use its VOR guidance and compatible DME distance information, while military TACAN equipment can use TACAN bearing and distance.
 
The nutshell: VOR gives direction, DME gives distance, TACAN gives military users direction and distance, and a VORTAC puts VOR and TACAN services at one site.
 
//////////////
🧭 Start With the Four Names
 
These facilities share some equipment and chart symbology, but the names tell us what service is available.
 
·  VOR: Direction
·  VOR/DME: Direction plus distance
·  TACAN: Military direction plus distance
· VORTAC: Civil VOR guidance and TACAN services at one site, including compatible distance information for properly equipped civil aircraft
 
This is FAA operational and training information, not a rule requiring a pilot to navigate with any one of these systems. The installed aircraft equipment, current charts, facility status, and the type of operation determine what can actually be used.
 
//////////////
📡 VOR: 360 Radials From the Station
 
A VOR station transmits very high frequency navigation signals in every direction. Those signals let compatible equipment determine the aircraft's magnetic bearing from the station.
 
The 360 courses extending outward are called radials. They are numbered from 001 through 360 and are always identified from the station.
 
For example:
·   The 090 radial extends east from the station.
·   The 180 radial extends south from the station.
·   An airplane can fly toward a VOR while located on a radial that is still named from the station.
 
That last distinction causes plenty of early confusion. TO or FROM describes the selected course relationship; the radial itself is always the magnetic bearing from the facility.

​//////////////
📏 DME Adds Distance
 
Distance measuring equipment answers a different cockpit question: How far are we from the station?
 
The aircraft's DME sends an interrogation to the ground equipment. The station replies, and the airborne unit converts the round-trip time into distance in nautical miles.
 
The important term is slant range:
·   DME measures the straight-line distance between the aircraft and the facility.
·   It does not directly show horizontal distance across the ground.
·   The difference is usually small when the aircraft is far from the station.
·   Close to or directly above the station, altitude becomes a noticeable part of the displayed distance.
 
A VOR/DME places the directional service and the distance service together. The paired equipment lets a pilot identify a position using both a radial and a distance.
 
//////////////
🎖️ TACAN: Military Bearing and Distance
 
TACAN stands for Tactical Air Navigation. It is a military ultra-high frequency system that provides:
· Azimuth: Direction or bearing
· Distance: DME-type slant-range information
 
A conventional civilian VOR receiver cannot use the TACAN azimuth signal. TACAN bearing and distance require compatible TACAN airborne equipment.
 
This is why it helps to separate the facility from the receiver. A ground site may transmit several services, but the aircraft only displays the services its installed equipment can receive.
 
//////////////
🔗 VORTAC: VOR and TACAN at One Site
 
A VORTAC combines VOR and TACAN equipment at one location as a unified navigation facility.
 
That one site supports different users:
·  VOR-equipped civil aircraft: Use the VOR azimuth guidance.
· VOR- and DME-equipped civil aircraft: Use VOR guidance plus compatible TACAN distance information.
·  TACAN-equipped military aircraft: Use TACAN azimuth and distance.
 
So the most accurate short definition is:
A VORTAC provides VOR azimuth, TACAN azimuth, and TACAN distance information from one integrated facility.
 
//////////////
🗺️ Read the Label on the Chart
 
On a VFR chart, the NAVAID information box identifies the type of facility. That label tells you whether the site is shown as a VOR, VOR/DME, VORTAC, or DME facility.
 
The box may also carry the facility name, frequency, identifier, Morse code, and operational notes. A DME-only facility is shown without a compass rose.

​During cross-country planning from Green Castle, don't stop at recognizing the compass rose. Read the entire information box and confirm:
·   Facility name and type
·   Frequency
·   Morse code identifier
·   Any voice capability shown
·   Current facility status and applicable NOTAMs
 
A chart symbol helps you find the information. It does not replace identifying the station or confirming that the facility is usable.
 
//////////////
🛰️ Why VOR Still Matters in a GPS Cockpit
 
GPS has changed how most pilots navigate, but the FAA continues to maintain a VOR Minimum Operational Network, or VOR MON, as a conventional backup during a GPS outage.
 
That makes VOR knowledge more than a historical exercise:
·   It gives pilots another way to confirm position and maintain situational awareness.
·   It supports conventional navigation when satellite service is disrupted.
·   It remains part of pilot certification standards.
·   It helps pilots understand the facilities and symbols still shown on current charts.
 
The VOR MON does not mean every old VOR remains available, and it does not eliminate normal preflight checks. Use current charts, the Chart Supplement, applicable NOTAMs, and current FAA information before relying on a facility.
 
//////////////
⚠️ Common Mix-Ups
 
·   Saying a radial points to the station. A radial extends from the station.
·   Treating DME as horizontal distance. DME displays slant range.
·   Assuming VOR automatically includes distance. A basic VOR provides azimuth, not DME.
·  Assuming a civilian VOR receiver can use TACAN bearing. It cannot without compatible TACAN equipment.
·  Treating VOR/DME and VORTAC as identical. Both can provide civil VOR and distance information, but a VORTAC also includes TACAN azimuth service.
·   Using a chart example or remembered frequency without checking current information.
 
The practical habit is simple: read the facility label, know what your aircraft can receive, identify the station, and verify that the signal is usable.
 
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🧩 The Big Takeaway
·   VOR: Direction through 360 magnetic radials extending from the station
·   VOR/DME: VOR direction plus slant-range distance
·   TACAN: Military bearing plus distance
·   VORTAC: VOR and TACAN services integrated at one site
 
Think of the information in two parts:
1) Where is the course? VOR or TACAN azimuth.
2) How far is the station? DME or TACAN distance.
 
Once those pieces are separated, the names stop looking like alphabet soup and start describing exactly what the facility provides.
 
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📚 FAA Sources and References
·   Aeronautical Information Manual, Chapter 1, Section 1, Navigation Aids: paragraphs 1-1-3, 1-1-5, 1-1-6, and 1-1-7
·   Pilot/Controller Glossary: entries for DME, Radial, TACAN, VOR, and VORTAC
·   Pilot's Handbook of Aeronautical Knowledge, Chapter 16, Navigation: pages 16-22, 16-24, and 16-28
·   FAA Aeronautical Chart Users' Guide: page 14, Radio Aids to Navigation
·   Private Pilot Airman Certification Standards, FAA-S-ACS-6C: Area VIII, Task F
·   Instrument Rating Airman Certification Standards, FAA-S-ACS-8C: Area II, Task B
·   Commercial Pilot Airman Certification Standards, FAA-S-ACS-7B: Area VI, Task B
·   FAA VOR Minimum Operational Network
 
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🗓️ Next Week
 
Regulations - Registration & Airworthiness Certificate
 
How long is an aircraft's registration and airworthiness certificate valid for?
 
Next week, we'll sort out:
·   Why an aircraft registration must be renewed every seven (7) years
·   Why a standard airworthiness certificate generally has no fixed expiration date
·   How registration, maintenance, and continued airworthiness work together
·   What responsibilities belong to the aircraft owner or operator
 
The key distinction is that one document has a renewal cycle, while the other remains effective only while its continuing conditions are met.