study guide
Detailed Study Guide for 14 CFR § 91.175 — Takeoff and Landing Under IFR
This section of the FARs explains the legal rules for using instrument approaches, descending below minimums, landing, going missed, IFR takeoff minimums, military-airport operations, RVR conversion, radar-vector procedures, procedure turns, and ILS components. It is one of the most practical IFR regulations because it governs the decision points that matter most during approach, landing, and departure in instrument conditions.
Headings and Subsection Headings
The main section heading is § 91.175 Takeoff and landing under IFR. The visible subsection headings are (a) Instrument approaches to civil airports, (b) Authorized DA/DH or MDA, (c) Operation below DA/DH or MDA, (d) Landing, (e) Missed approach procedures, (f) Civil airport takeoff minimums, (g) Military airports, (h) Comparable values of RVR and ground visibility, (i) Operations on unpublished routes and use of radar in instrument approach procedures, (j) Limitation on procedure turns, and (k) ILS components. The later headings continue with (e) through (k) exactly as shown in the regulation text. The section appears within Title 14 — Aeronautics and Space, Subpart B — Flight Rules, under Instrument Flight Rules.
What the Rule Is Really About
At a practical level, § 91.175 tells you four major things: which approach procedure you must use, what minimums control, when you may continue below DA/DH or MDA, and when you must abandon the approach and execute a missed approach. It also adds important operating rules for IFR takeoffs, military airports, radar vectors, “No PT” situations, and the components that make up an ILS.
(a) Instrument Approaches to Civil Airports
When an instrument approach is necessary at a civil airport, the pilot must use the standard instrument approach procedure prescribed in Part 97 for that airport unless the FAA authorizes otherwise. In plain language, that means you do not get to invent your own approach path or substitute some informal method just because conditions seem manageable. This paragraph specifically does not apply to United States military aircraft.
A good memory phrase is: civil airport + IFR approach = use the published Part 97 procedure unless FAA says otherwise. That makes subsection (a) the basic legal foundation for flying published instrument approaches into civilian fields.
(b) Authorized DA/DH or MDA
If the procedure requires a DA/DH or MDA, the authorized minimum is the highest of three values: the published approach minimum, the minimum prescribed for the pilot in command, and the minimum appropriate for the aircraft equipment being used on that approach. This is extremely important because the regulation does not allow you to choose the lowest number available; it requires you to use the most restrictive applicable one.
In practice, subsection (b) means legal minimums are not just what is printed on the chart. Pilot qualifications and aircraft equipment can raise the minimum you must use even when the published procedure itself shows a lower value. The best way to memorize this is: authorized minimum = highest of the three.
(c) Operation Below DA/DH or MDA
This is one of the most tested and operationally significant parts of the section because it governs when you may descend below approach minimums. Except as provided in § 91.176, a pilot may not go below the authorized MDA or continue below the authorized DA/DH unless all required conditions are satisfied.
The first requirement is that the aircraft must be continuously in a position from which a normal descent to landing on the intended runway can be made using normal maneuvers. For operations under Parts 121 and 135, that descent must also permit touchdown within the runway touchdown zone. This means the airplane cannot be too high, too fast, too far off centerline, or otherwise so unstable that a normal landing is no longer realistically available.
The second requirement is visibility. Flight visibility must be at least the visibility prescribed in the standard instrument approach being used. Reaching DA/DH or MDA alone is therefore not enough to continue; the visibility requirement must also be met.
The third requirement is visual reference. At least one approved visual reference for the intended runway must be distinctly visible and identifiable to the pilot, except where Category II or III requirements are otherwise specified by the Administrator. The regulation lists acceptable references as the approach light system, threshold, threshold markings, threshold lights, runway end identifier lights, visual glideslope indicator, touchdown zone or touchdown zone markings, touchdown zone lights, runway or runway markings, and runway lights. The list continues with runway end identifier lights, visual glideslope indicator, touchdown zone references, runway markings, and runway lights, all of which may satisfy the visual-reference requirement when distinctly visible and identifiable.
A particularly important special rule applies if the pilot is using the approach light system as the only visual reference. In that case, the pilot may not descend below 100 feet above the touchdown zone elevation unless the red terminating bars or red side row bars are also distinctly visible and identifiable. This is a classic checkride and written-test point because many pilots remember “approach lights count,” but forget that they do not authorize descent below 100 feet above TDZE by themselves.
The high-yield way to study subsection (c) is to memorize the three-part test for descending below minimums: position, visibility, and visual reference. If any one of those is missing, continuing below DA/DH or MDA is not legal under this section.
(d) Landing
Subsection (d) answers a slightly different question from subsection (c): even if you reached the runway environment, when is landing actually prohibited? The rule says that, except for U.S. military aircraft, no pilot may land when the required visual conditions are not satisfied. For operations conducted under § 91.176, the visual-reference requirements of that section must be met. For all other operations under Part 91 and Parts 121, 125, 129, and 135, the flight visibility may not be less than the visibility prescribed in the standard instrument approach procedure being used.
The practical takeaway is that landing legality depends on more than simply touching down after breaking out. If the required conditions are missing, the landing is not permitted even if the runway becomes visible late in the approach. A good study phrase is: no required visual conditions = no legal landing.
(e) Missed Approach Procedures
This subsection tells you when the missed approach is mandatory, and it requires immediate action. Except for U.S. military aircraft, the pilot must immediately execute an appropriate missed approach whenever the requirements of paragraph (c) or § 91.176 are not met while below MDA, upon arrival at the missed approach point, at DA/DH when one is specified and required, and at any time after that until touchdown. In other words, if the required conditions are not there at the decision point, you do not continue “just a little farther” to see if things improve.
The regulation also addresses circling approaches. During a circling maneuver, if an identifiable part of the airport is not distinctly visible to the pilot, an immediate missed approach is required unless the temporary loss of sight is caused only by a normal bank of the aircraft during the circling approach. That exception matters because a normal turn can briefly interrupt direct sight of the airport without making the circling approach automatically illegal.
The best way to memorize subsection (e) is this: if the required conditions are not met below minimums or at the decision point, go missed immediately. For circling, remember: lose the airport, go missed—unless the loss is only due to normal bank.
(f) Civil Airport Takeoff Minimums
Subsection (f) applies specifically to persons operating under Parts 121, 125, 129, and 135. Unless the FAA authorizes otherwise, no pilot may take off IFR from a civil airport unless the weather at takeoff is at or above the IFR takeoff minimums published for that airport under Part 97. This means the section does not create a universal one-size-fits-all takeoff minimum first; it first looks to published takeoff minimums.
If no takeoff minimums are published for the airport, the regulation provides default minimums. For aircraft other than helicopters with two engines or less, the default is 1 statute mile visibility. For aircraft with more than two engines, the default is 1/2 statute mile visibility. For helicopters, the default is also 1/2 statute mile visibility.
Another important rule concerns obstacle departure procedures. If an ODP is published for the departure runway, the pilot must use that ODP or an alternative procedure or route assigned by ATC, except as provided in paragraph (f)(4). Paragraph (f)(4) adds that Part 121 and Part 135 operators must use a takeoff obstacle clearance or avoidance procedure that ensures compliance with the applicable airplane performance operating limitations, while Part 129 operators must use a procedure that ensures compliance with the performance operating limitations prescribed by the operator’s State.
For study purposes, subsection (f) contains one of the easiest number sets to memorize in all of IFR regulations: 1 mile / 1/2 mile / 1/2 mile. That shorthand stands for two engines or less = 1 SM, more than two engines = 1/2 SM, and helicopters = 1/2 SM when no published takeoff minimums exist.
(g) Military Airports
When a civil aircraft operates IFR into or out of a military airport, it must comply with the instrument approach procedures and the takeoff and landing minimums prescribed by the military authority having jurisdiction over that airport, unless the Administrator prescribes otherwise. This subsection is short, but operationally important, because it makes clear that military fields may impose controlling procedures and minimums for civil IFR operations there.
The memory aid here is straightforward: civil aircraft at a military airport must follow the military field’s IFR procedures and minimums unless the Administrator says otherwise.
(h) Comparable Values of RVR and Ground Visibility
Subsection (h) explains what to do when RVR minimums are published but RVR is not actually reported for the intended runway. Except for Category II and Category III minimums, the pilot must convert the RVR minimum to ground visibility using the table in paragraph (h)(2), and that converted value becomes the applicable visibility minimum for takeoff or landing on that runway. The exception for Category II and III is important because the conversion rule does not apply to those minimums.
The table gives the following equivalencies: 1,600 RVR = 1/4 mile, 2,400 = 1/2 mile, 3,200 = 5/8 mile, 4,000 = 3/4 mile, 4,500 = 7/8 mile, 5,000 = 1 mile, and 6,000 = 1 1/4 miles. These values are worth memorizing because they are directly stated by the regulation and may be needed whenever RVR is unavailable.
A good study strategy is to focus first on the most common anchor values: 1600 = 1/4, 2400 = 1/2, 4000 = 3/4, and 5000 = 1 mile. Once those are familiar, the intermediate values are easier to remember.
(i) Operations on Unpublished Routes and Use of Radar in Instrument Approach Procedures
This subsection explains how radar may be used and what altitude rules apply when vectored or operating on unpublished routes. When radar is approved for ATC purposes, it may be used not only for surveillance and precision radar approaches, but also in conjunction with instrument approach procedures based on other radio navigational aids. Radar vectors may be used to provide course guidance through approach segments to the final course or fix.
The key operational rule is the altitude requirement after approach clearance. When operating on an unpublished route or while being radar vectored, the pilot must maintain the last assigned altitude until the aircraft is established on a segment of a published route or instrument approach procedure, unless ATC assigns a different altitude. After the aircraft is established on that published segment, the published altitudes govern descent through each succeeding segment unless ATC assigns otherwise.
Upon reaching the final approach course or fix, the pilot may either complete the instrument approach under the approved procedure for the facility or continue a surveillance or precision radar approach to landing. The study takeaway is: vectored or unpublished route = maintain last assigned altitude until established; once established, published altitudes apply.
(j) Limitation on Procedure Turns
Subsection (j) is a classic IFR trap area because some pilots still think a procedure turn is always available if charted. The regulation says a pilot may not make a procedure turn unless ATC clears it in three situations: when radar vectored to a final approach course or fix, when flying a timed approach from a holding fix, or when the procedure says “No PT”.
That means the presence of a depicted course-reversal area does not automatically authorize flying it when one of those conditions exists. The memory line here is short and effective: radar vector, timed approach, or “No PT” = no procedure turn unless ATC clears it.
(k) ILS Components
The regulation identifies the basic components of an ILS as the localizer, glide slope, and outer marker, and it adds that an inner marker is included when installed for Category II or Category III instrument approach procedures. This makes subsection (k) especially useful for oral-exam style questions about the legal structure of a basic ILS.
The rule also states that the outer marker may be substituted by a compass locator, PAR or ASR, DME, VOR, or nondirectional beacon fixes authorized in the standard instrument approach procedure, or a suitable RNAV system used with a fix identified in the standard instrument approach procedure. For Category II or III operations, the applicability of and substitution for the inner marker is determined by the appropriate Part 97 approach procedure, a letter of authorization, or operations specifications issued to the operator.
A simple memory tool is LGO: Localizer, Glide slope, Outer marker. Then remember that Category II/III may add an inner marker, and that several approved fixes or systems may substitute for the outer marker when the procedure allows it.
Best High-Yield Memorization Points
The single most important memory item in § 91.175 is the three-part test for descending below minimums: normal position to land, required flight visibility, and at least one required visual reference. The second major memory item is the missed approach rule: if the conditions are not met below MDA, at DA/DH, at the MAP, or after that before touchdown, execute the missed approach immediately. The third is the unpublished takeoff minimum default: 1 SM for two engines or less, 1/2 SM for more than two engines, and 1/2 SM for helicopters.
Other high-yield points include the approach-light limitation below 100 feet above TDZE. Another is the radar-vector altitude rule: maintain the last assigned altitude until established on a published segment. Another is the procedure-turn limitation: no PT when vectored, timed, or charted “No PT” unless ATC specifically clears it. Finally, remember the basic ILS components and the fact that the outer marker may be replaced by certain approved substitutes.
Quick Self-Test
Ask yourself whether you can state from memory the three conditions required to continue below DA/DH or MDA. Make sure you can recite the default IFR takeoff minimums when none are published. Make sure you know exactly when a missed approach becomes mandatory. Make sure you can identify the situations in which a procedure turn is prohibited without ATC clearance. Also make sure you can name the basic ILS components and at least two valid substitutes for the outer marker.
One-Paragraph Wrap-Up
In full, § 91.175 is the core IFR regulation that tells a pilot which published approach to use, how to determine the controlling minimums, what must be present to descend below DA/DH or MDA, when landing is prohibited, when a missed approach is mandatory, what takeoff minimums apply, how civil aircraft operate at military fields, how to convert RVR to ground visibility, how to handle vectors and unpublished-route altitudes, when procedure turns are barred, and what legally counts as the components of an ILS. If you master this one section thoroughly, you will understand many of the most important legal decision points in IFR flying.
Would you like me to turn this into a one-page checkride cram sheet or a flashcard set, and feel free to ask if you’d like more detail.