14.2 14 CFR 91.175 Landing Minimums & Visual References
Key Takeaways
- Under 14 CFR § 91.175(c), a pilot may not operate below the Decision Altitude (DA/DH) or Minimum Descent Altitude (MDA) unless three conditions are met simultaneously: normal descent/maneuvers, required flight visibility, and distinctly identifiable visual references.
- Flight visibility—as determined solely by the pilot looking out from the cockpit—is the legally controlling visibility standard for descending below DA/MDA under Part 91.
- The Approach Light System (ALS) permits descent down to 100 feet above Touchdown Zone Elevation (TDZE); descent below 100 ft requires distinct identification of the red terminating bars (ALSF-1) or red side row bars (ALSF-2), or one of the other 9 runway references.
- The 10 approved visual references under § 91.175(c)(3) are: (1) ALS, (2) Threshold, (3) Threshold markings, (4) Threshold lights, (5) REIL, (6) Visual glideslope indicator (VASI/PAPI), (7) Touchdown zone or markings, (8) Touchdown zone lights, (9) Runway or runway markings, and (10) Runway lights.
- Attempting to descend below DA/MDA without all three § 91.175(c) requirements satisfied, or 'ducking under' the glidepath upon first sighting lights, is a primary causal factor in Controlled Flight Into Terrain (CFIT).
14 CFR 91.175 Landing Minimums & Visual References
Quick Answer: Under 14 CFR § 91.175(c), a pilot may descend below the Decision Altitude (DA/DH) or Minimum Descent Altitude (MDA) ONLY when three conditions are met simultaneously: (1) The aircraft is in a continuous position to make a normal descent to landing using normal maneuvers, (2) The flight visibility (from the cockpit) is at or above published approach minimums, and (3) At least one of 10 approved visual references is distinctly visible and identifiable. The Approach Light System (ALS) permits descent down to 100 feet above Touchdown Zone Elevation (TDZE), but descending below 100 ft requires either the red terminating bars (ALSF-1), red side row bars (ALSF-2), or one of the other 9 runway environment references in sight.
The transition from flying on instrument reference inside the clouds to hand-flying a visual landing in low visibility is the most safety-critical phase of an instrument flight. To prevent accidents caused by pilots descending blindly into fog or terrain, the Federal Aviation Administration established 14 CFR § 91.175(c), strictly governing when an aircraft may descend below instrument minimums.
The Three Legal Pillars of 14 CFR § 91.175(c)
No pilot may operate an aircraft below the authorized DA/DH or MDA unless all three of the following requirements are met simultaneously:
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| THE THREE MANDATORY PILLARS OF 14 CFR § 91.175(c) |
| |
| ┌────────────────────────┬────────────────────────┬────────────────────────┐ |
| │ PILLAR 1 │ PILLAR 2 │ PILLAR 3 │ |
| │ NORMAL DESCENT │ FLIGHT VISIBILITY │ VISUAL REFERENCES │ |
| ├────────────────────────┼────────────────────────┼────────────────────────┤ |
| │ Aircraft continuously │ Flight visibility (from│ At least ONE of the │ |
| │ in a position from │ cockpit) is NOT less │ 10 approved visual │ |
| │ which descent to land │ than the visibility │ references for intended│ |
| │ can be made at normal │ prescribed in the │ runway is distinctly │ |
| │ rate using normal │ standard instrument │ visible and │ |
| │ maneuvers. │ approach being used. │ identifiable. │ |
| └────────────────────────┴────────────────────────┴────────────────────────┘ |
| |
| ALL THREE CONDITIONS MUST BE SATISFIED CONTINUOUSLY! |
| If ANY condition fails -> IMMEDIATE MISSED APPROACH REQUIRED |
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Pillar 1: Position for Normal Descent & Normal Maneuvers (§ 91.175(c)(1))
- The aircraft must continuously remain in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers.
- For commercial operations under 14 CFR Part 121 and Part 135, the descent rate must allow touchdown to occur within the Touchdown Zone (TDZ) (the first 3,000 feet or first one-third of the runway length, whichever is less).
- Prohibited Actions: Steep diving turns, S-turns across final, aggressive pitch-down maneuvers, or excessive descent rates ($> 1,000\text{ FPM}$ in light aircraft) to salvage an unstabilized approach.
Pillar 2: Flight Visibility Not Less Than Minimums (§ 91.175(c)(2))
- The flight visibility (the average forward horizontal distance from the cockpit of an aircraft in flight at which prominent unlighted objects may be seen by day and lighted objects by night) must be at or above the published visibility minimum on the approach chart.
- Cockpit Flight Visibility vs. Ground Visibility:
- Automated ground sensors (ASOS/AWOS) and Runway Visual Range (RVR) report visibility at surface ground stations.
- Under 14 CFR Part 91, the legally controlling visibility standard when deciding to descend below DA/MDA is the actual flight visibility observed by the pilot in command from the cockpit looking forward along the approach path.
Pillar 3: Distinctly Identifiable Visual References (§ 91.175(c)(3))
- The pilot must have at least one of the 10 specific visual references approved by regulation for the intended runway distinctly visible and identifiable.
The 10 Approved Visual References (14 CFR § 91.175(c)(3))
The FAA explicitly enumerates ten approved visual references. Spotting any item outside this list (e.g., taxiways, airport beacon, terminal buildings, city streets) does NOT legally permit descent below DA/MDA!
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| THE 10 APPROVED VISUAL REFERENCES UNDER § 91.175(c)(3) |
| |
| 1. Approach Light System (ALS) ──► Descent permitted to 100 ft above TDZE ONLY |
| (Must see Red Terminating or Side Row bars |
| to descend below 100 ft using ALS). |
| |
| RUNWAY THRESHOLD ENVIRONMENT: |
| 2. The Threshold |
| 3. The Threshold Markings |
| 4. The Threshold Lights |
| 5. Runway End Identifier Lights (REIL) |
| |
| DESCENT PATH & TOUCHDOWN ZONE: |
| 6. Visual Glideslope Indicator (VASI / PAPI) |
| 7. Touchdown Zone or Touchdown Zone Markings |
| 8. Touchdown Zone Lights |
| |
| RUNWAY SURFACE & EDGE: |
| 9. Runway or Runway Markings |
| 10. Runway Lights (Edge / Centerline) |
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Comprehensive Breakdown of the 10 Visual References:
| Reference # | Visual Component | Description & Visual Identification |
|---|---|---|
| 1 | Approach Light System (ALS) | High/medium intensity light sequence (e.g., ALSF-1, ALSF-2, MALSR). Special 100-ft limitation applies. |
| 2 | The Threshold | The physical beginning of the portion of the runway usable for landing. |
| 3 | The Threshold Markings | Standardized longitudinal white stripes ("piano keys") marking the beginning of landing pavement. |
| 4 | The Threshold Lights | A transverse row of green lights marking the landing threshold across the runway end. |
| 5 | Runway End Identifier Lights (REIL) | A pair of synchronized flashing white strobe lights located on each side of the runway threshold. |
| 6 | Visual Glideslope Indicator | Visual approach slope indicator (VASI) or precision approach path indicator (PAPI) providing vertical visual guidance. |
| 7 | Touchdown Zone or TDZ Markings | Pairs of rectangular white bars painted symmetrically on each side of the runway centerline in the first 3,000 ft. |
| 8 | Touchdown Zone Lights | Two rows of transverse white light bars flush-mounted in the runway surface extending 3,000 ft down the runway. |
| 9 | Runway or Runway Markings | The physical paved runway surface, white runway centerline stripes, or runway side stripes. |
| 10 | Runway Lights | Elevated or flush white runway edge lights and embedded white/red runway centerline lights. |
The Approach Light System (ALS) & The 100-Foot Rule
Among all ten visual references, the Approach Light System (ALS) has a unique legal limitation under § 91.175(c)(3)(i):
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| THE ALS 100-FOOT RULE DECISION FLOW |
| |
| Aircraft at DA/DH or MDA |
| │ |
| ▼ |
| Are Approach Lights (ALS) in sight? |
| │ |
| ┌────────────────┴────────────────┐ |
| ▼ YES ▼ NO |
| [ DESCEND TO 100 FT ] [ EXECUTE MISSED APPROACH ] |
| (100 ft above TDZE limit) |
| │ |
| ▼ |
| Passing 100 ft Above TDZE: |
| Are RED BARS visible OR any of the other 9 runway references in sight? |
| │ |
| ┌───────┴───────┐ |
| ▼ YES ▼ NO |
| [ LAND ] [ GO MISSED ] |
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The 100-Foot Limitation Explained
- If the pilot acquires ONLY the approach light system at Decision Altitude (DA) or Minimum Descent Altitude (MDA), the pilot is legally authorized to continue descending down to 100 feet above the Touchdown Zone Elevation (TDZE).
- Reasoning: Approach light systems extend $1,400\text{ to } 2,400\text{ feet}$ out from the threshold into the approach corridor. Sighting the white lead-in lights confirms the aircraft is laterally aligned with the extended centerline, but it does not prove the aircraft has reached the paved runway surface!
Descending Below 100 Feet Above TDZE
Under § 91.175(c)(3)(i), the pilot may not descend below 100 feet above TDZE using the approach lights alone, UNLESS:
- The red terminating bars (present on ALSF-1 systems) are distinctly visible and identifiable, OR
- The red side row bars (present on ALSF-2 systems) are distinctly visible and identifiable, OR
- At least one of the other 9 runway environment visual references (such as the threshold, threshold lights, REIL, PAPI, TDZ lights, or runway edge lights) is distinctly visible and identifiable.
System Differences: ALSF vs. MALSR / ODALS
- ALSF-1 & ALSF-2 (High-Intensity Category II/III Systems): Feature red terminating bars (a horizontal bar of red lights at the inner 200 ft) or red side row bars (two parallel rows of red light bars flanking the centerline in the inner 1,000 ft). Sighting these red bars authorizes descent all the way to touchdown!
- MALSR, SSALR, MALS, and ODALS: Simplified medium-intensity systems widely installed at regional airports DO NOT HAVE RED BARS.
- Critical Takeaway: If flying an approach with a MALSR or ODALS, sighting the approach lights alone only gets you down to 100 feet above TDZE. If you do not acquire the runway threshold or runway lights by 100 ft AGL, you MUST immediately execute a missed approach!
Visual Illusions & "Duck-Under" Hazards
When transitioning from instrument scan to visual references in low visibility, pilots are susceptible to severe optical illusions that have caused numerous fatal accidents:
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| THE DANGEROUS "DUCK-UNDER" PHENOMENON |
| |
| 1. Pilot breaks out at DA/MDA and catches first glimpse of approach lights. |
| 2. Due to restricted visibility, the runway appears farther away or higher than it is. |
| 3. Pilot pushes the nose down ("ducks under") to stay visual beneath the cloud base. |
| 4. Aircraft penetrates the obstacle clearance surface short of the runway and strikes |
| approach light towers, trees, power lines, or terrain! |
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Common Visual Illusions Near Landing Minimums:
- Featureless Terrain / Black Hole Illusion: Approaching over water or dark, unlit terrain at night creates the illusion of being too high, causing pilots to fly an excessively low approach.
- Runway Width Illusion: A narrower-than-usual runway creates the illusion that the aircraft is higher than actual, inducing a low approach. A wider runway creates the illusion of being too low, inducing a flare that is too high.
- Sloping Runway Illusion: An up-sloping runway creates the illusion of being too high (leading to a low approach); a down-sloping runway creates the illusion of being too low.
- Atmospheric Illusions (Haze and Fog): Flying into haze or fog creates the illusion of being higher and farther from the runway than actual, tempting the pilot to push the nose down aggressively.
[!TIP] Cockpit Best Practice: Never "duck under" the electronic or visual glideslope. Cross-check your PAPI/VASI and flight instruments continuously down to the flare. If the PAPI shows more than two red lights (low), immediately correct with pitch and power or execute a go-around!
Under 14 CFR § 91.175(c), which of the following visual references alone does NOT authorize a pilot to descend below 100 feet above the Touchdown Zone Elevation (TDZE)?
What three conditions must be satisfied simultaneously under 14 CFR § 91.175(c) before a pilot may operate an aircraft below the published Decision Altitude (DA) or Minimum Descent Altitude (MDA)?
Which of the following items is NOT an approved visual reference under 14 CFR § 91.175(c)(3) to descend below DA/MDA?