Fly a 3-degree descent path with the 318 ft-per-NM rule, groundspeed × 5 rate, threshold altitude checks, PAPI/VASI cues and go-around limits.
To fly a 3-degree descent path, aim to lose about 318 feet per nautical mile, measured towards the landing threshold. Start near groundspeed × 5 feet per minute, use × 5.3 for the closer value, then make small power and pitch corrections from PAPI, VASI, glideslope, glidepath or altitude-distance checks.
For Aviation & Real-World Flying, we treat three degrees as a conventional approach angle, not a requirement for every runway. A published approach angle, charted altitude, aircraft limitation or operating procedure takes precedence over this generic calculation.
What does 3 degrees mean in aviation?
In aviation, a 3-degree descent means that the flight path is angled three degrees below horizontal. That equals a gradient of about 5.24% and a height change of approximately 318.4 feet per nautical mile.
The terms are often mixed in simulator discussions, but an ILS provides a glideslope, an RNAV approach may provide a glidepath, and a visual approach follows an aiming path supported by PAPI or VASI lights. All can be close to three degrees, but the published angle may be steeper or shallower.
What altitude should I be at on a 3-degree approach?
Your target altitude is approximately 318 feet for every nautical mile remaining, plus threshold elevation and the planned threshold-crossing height.
target altitude MSL = threshold elevation + threshold-crossing height + (distance to threshold in NM × 318.4)
For example, with a threshold elevation of 600 feet and a 50-foot threshold-crossing height, the target at 5 NM is approximately 600 + 50 + 1,592 = 2,242 feet MSL.
| Distance to landing threshold | Path height above threshold elevation |
|---|---|
| 10 NM | About 3,234 ft |
| 5 NM | About 1,642 ft |
| 3 NM | About 1,005 ft |
| 1 NM | About 368 ft |
| At the threshold | 50 ft |
This table assumes a 50-foot threshold-crossing height. Use the charted TCH, PAPI angle or minimum eye height over threshold when one is specified. These values describe the guidance path at the aircraft antenna or pilot's eye; they do not guarantee the same wheel clearance for every aircraft.
Why is a 3-degree glide slope about 318 feet per NM?
A 3-degree glide slope falls 318.4 feet over the 6,076 feet in one nautical mile.
6,076 × tan(3°) = 318.4 feet
The familiar 318 feet figure is therefore geometry, not an arbitrary aviation rule. Check the origin of the distance shown by the simulator: DME from an offset antenna, distance to an airport reference point and distance to a displaced landing threshold can all produce different altitude checks.
What vertical speed gives a 3-degree descent rate?
A 3-degree descent requires approximately groundspeed × 5.3 feet per minute. The quicker groundspeed × 5 rule is a useful initial setting, although it underestimates the geometric value by about 6%.
vertical speed in ft/min = groundspeed in knots × 5.3
| Groundspeed | Approximate 3-degree descent rate |
|---|---|
| 60 kt | 320 ft/min |
| 90 kt | 480 ft/min |
| 100 kt | 530 ft/min |
| 120 kt | 640 ft/min |
| 140 kt | 740 ft/min |
| 160 kt | 850 ft/min |
Use groundspeed, not indicated airspeed. At the same indicated speed, a headwind reduces the required rate while a tailwind increases it. Recalculate after a substantial speed or wind change, and remember that many vertical-speed displays show descent as a negative value.
For additional speeds and the exact trigonometric method, see our worked approach descent-rate calculations.
Where should the initial descent begin?
Begin the final descent where your level altitude meets the calculated path, unless the published procedure specifies a different intercept point.
distance from threshold = (height above threshold elevation − TCH) ÷ 318.4
If the aircraft is level 3,000 feet above threshold elevation and the TCH is 50 feet, the path reaches that altitude about 9.3 NM from the threshold. For an ILS, intercept the glideslope from below at the charted altitude rather than descending early or diving onto it from above.
This final-approach calculation is not the same as planning an en-route top of descent. The common 3-to-1 rule allows roughly 3 NM for each 1,000 feet to lose; our 3-to-1 top-of-descent method also accounts for deceleration and restrictions.
How do I fly the 3-degree path step by step?
Fly the path by establishing a stable final approach, selecting an initial vertical speed and correcting from guidance rather than trying to hold one fixed number.
- Brief the correct threshold and angle. Note threshold elevation, any displaced threshold, the published approach angle, TCH and the source of your distance information.
- Set the altimeter and establish final track. Complete the planned configuration changes early enough that gear, flap and speed changes do not create a large path upset near the runway.
- Intercept the path correctly. Follow charted ILS or RNAV guidance where available. For a visual approach, use PAPI, VASI, altitude-distance checks and a stable runway aiming point.
- Set the initial descent rate. Multiply groundspeed by 5.3, or use × 5 for quick mental arithmetic. At 120 knots groundspeed, begin near 640 ft/min.
- Trim and cross-check. Monitor approach speed, vertical guidance, distance and altitude together. Vertical speed predicts the path; the glideslope, glidepath or visual indication confirms the result.
- Make small corrections. Correct trends before they become large deviations, then allow the aircraft time to respond instead of reversing the input immediately.
- Flare for the aircraft type. The 3-degree line is an approach path, not a line flown through the runway. Transition to the aircraft-specific flare and touchdown technique near the surface.
How should I correct a high or low approach?
Correct a small path error with coordinated power and pitch changes while protecting the target speed. If high, reduce power as appropriate and allow a modestly greater descent rate; if low, add power and shallow the descent.
In many light aircraft, power is the convenient path-control input while pitch protects speed. Jets, autothrottles and automated flight-control systems may use different pitch-and-thrust logic, so “pitch for speed, power for path” is not an absolute rule. Follow the aircraft procedure and avoid aggressive corrections close to the ground.
How can I tell if I am above or below the glidepath?
Use the vertical guidance trend rather than waiting for a large deviation. A standard four-light PAPI shows two white and two red lights on path, more white when high and more red when low.
- PAPI: two white and two red is on path; three or four white is high; three or four red is low.
- VASI: red over white is normally on path, white over white is high and red over red is low.
- ILS or RNAV guidance: keep the vertical deviation centred with small corrections. Chasing the indicator usually creates alternating high and low deviations.
- Visual aiming point: the selected point should remain nearly stationary in the windscreen. If it rises, you are tending to undershoot; if it moves down, you are tending to overshoot.
A 50-foot threshold-crossing height on a 3-degree path projects back to an aiming point roughly 1,000 feet beyond the threshold. Flare, cockpit eye height and aircraft size determine where the wheels actually touch down. Our visual-approach walkthrough covering PAPI/VASI, aiming points and speed control explains the complete sight picture.
What does runway threshold mean in MSFS and X-Plane?
The runway threshold in MSFS or X-Plane is the beginning of the runway portion available for landing in that direction, not necessarily the first paved surface. A displaced threshold is marked farther along the runway, and approach distance and crossing-height calculations must use that displaced point.
Use the normal cockpit pilot-eye position when reading PAPI or VASI lights. An external, drone or incorrectly positioned custom cockpit camera can show a different light indication because the simulated viewpoint is higher, lower or laterally displaced.
Scenery, navigation data and approach coding can occasionally disagree, particularly after mixing airport add-ons with a different navigation-data source. If the PAPI and electronic glidepath do not align, do not chase both or average the indications. Verify the published angle, runway threshold, scenery compatibility and navigation data, then choose the guidance appropriate to the approach being flown.
Does this method apply to Learn to Fly 3?
No. Learn to Fly 3 is an arcade-style game rather than a procedural aviation simulator, so real 3-degree approach calculations are not its intended mechanic. The geometry does apply in Microsoft Flight Simulator and X-Plane when the aircraft, runway and approach guidance model conventional aviation procedures.
Readers seeking a complete manual (完全マニュアル) should treat this as a focused landing-path technique, not a replacement for the aircraft checklist, POH or AFM, approach chart and type-specific operating procedures.
What causes an unstable 3-degree approach?
Most unstable approaches begin with incorrect distance, speed or configuration assumptions rather than a failure to calculate 318 feet per nautical mile.
- Using indicated airspeed: calculate vertical speed from groundspeed so the wind component is included.
- Measuring from the wrong point: confirm that distance is to the landing threshold, especially with DME offsets or displaced thresholds.
- Mixing MSL and height above threshold: add threshold elevation and TCH when comparing the path with indicated altitude.
- Holding one vertical speed: update the rate when groundspeed changes and use path guidance as feedback.
- Chasing the indication: make one small correction, wait for the trend and then reassess.
- Capturing from above: a steep dive to regain an ILS glideslope can produce excessive speed and descent rate. Intercept from below unless the procedure specifically directs otherwise.
- Configuring late: gear, flap and thrust changes close to the runway can displace the aircraft from both speed and path.
- Forcing three degrees: use the published angle when terrain, obstacles, runway geometry or local procedure requires something different.
When should I stop correcting and go around?
Go around when the approach is not stabilised by the applicable gate or recovering the path would require large pitch, power, bank, speed or descent-rate changes. A late dive from above or a low-speed pull-up from below is not a safe path correction.
Many operators use stabilised-approach gates around 1,000 feet above touchdown in instrument conditions and 500 feet in visual conditions, but the applicable aircraft and operator criteria control. For simulator practice, brief the gate before starting the approach and apply it consistently rather than deciding after the approach has deteriorated.
If the gate is missed, follow a positive simulator go-around and missed-approach procedure instead of trying to rescue the landing close to the runway.