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Non-precision Approaches
VOR--NDB--GPS--LOC--ASR--LDA--SDF approaches do not have vertical reference other than the altimeter and the direction of the approach may not be aligned with the runway. You will be expected to maneuver for the landing. The minimum descent altitude (MDA) may be very near the low IFR altitude of weather. The MDA may be relatively high depending on distance, terrain, and type of approach. You cannot leave the MDA without seeing the runway. Just seeing the ground is NOT enough.

The design limits of the system set the minimums. The approach is named by the navaid and runway at the airport. The navaid may be before, beside, on, or beyond the airports. A margin of error is built into the plate by TERPS (rules for making approaches) but the expectation is that the pilot will fly the procedure perfectly so as to maintain these safety margins. The non-precision approach usually does not parallel the runway centerline; instead the electronic line takes us to the end of the runway at an angle. There is no electronic vertical guidance. A turning maneuver is going to be required for landing. The MDA will vary with the terrain, lighting available and system used

A pilot has a choice of doing the approach with vectors or as 'own-nav'. Vectors are easier since ATC usually sets you up with a 30-degree intercept to your inbound course. Your 'own-nav' may require that you reverse your direction of arrival. This means using a procedure turn or a holding pattern to make the turn-around, and begin your descent when established. There are required reports at the fix inbound and when established from the procedure turn.

The chart will have course, altitudes, frequencies and times for you to utilize during the approach. The approach is segmented into three parts:
1. Initial segment gets you lined up for the approach.
2. Intermediate segment usually begins the descent.
3. Final segment gives you a timing point, minimum descent(s), and missed approach point.
4. Missed segment which begins at the missed approach point with a direction, and climb required.

A non-precision approach has four segments; each segment begins at a defined point. The initial approach segments begins at the IAF. At the intermediate approach segment you are established on course and descending. The final approach segment usually has a FAF but not always from which time or DME is used to guide the descent to the MDA. You do not leave the MDA until seeing the runway. The fourth segment is from the missed approach to the missed approach fix. The route and altitudes for each segment are shown in plan and profile views. By flying the published headings and altitudes you are protected from obstacles.

Being "Cleared for the Approach" by ATC means that you can follow the published procedure. By following the publish routes at the published altitudes you are 'guaranteed' not to hit any ground object. That is, providing you have correctly set your altimeter. Historically the 'chop and drop' has been the accepted procedure and could be used in familiar situations. Otherwise, the stabilized approach using the airspeed, time, and descent rate is to be preferred. Descent from the FAF to the MDA have traditionally been of the 'chop and drop' type but today the use of DME makes stabilized descents more common. The VDP (visual descent point) either created or charted makes it possible for the pilot to prepare for a landing for straight in approaches.

The purpose of the non precision approach is not to put you on the runway. Its purpose is to get you down out of the clouds and in sight of the runway. The pilot is expected to navigate to the missed approach point. Only if clear of the clouds will he will be allowed to maneuver visually to the runway. MDA are usually below standard pattern altitudes and will require a higher level of maneuvering skill. Practice your short approaches in better conditions.

If you descend to the MDA and see the runway but not in time to make a normal landing, you must climb to circling minimums before turning. In the turns you are required to keep the airport in sight at all times. You do not descend below circling minimums again until lined up with the visible runway. Non-precision approaches at night should only be flown if there is a VASI. If at first you do not succeed…quit and go to a better place. Most approach accidents occur during the second attempt.

You can use or make a visual descent point (VDP) as a landing aid. TERPs require a VDP for all straight-in non-precision approaches except for procedures with remote altimeter setting, where the descent path is below a required step-down altitude and where it would be between the MAP and runway. No VDP will exist where an obstacle exists. The absence of a VDP serves as an obstacle alert.

The VOR and NDB approaches do not have the options of precision approaches. Only Minimum Decent Altitudes exist. The circle to land minimums have Height Above Airport numbers parenthetically rather than runway numbers. The circle to land altitude and distance is determined by aircraft category speed. For straight-in minimums there are three requirements:
1. Approach aligned within 30-degrees
2. Approach must cross the runway threshold
3. Descent gradient cannot exceed 400 feet per nautical mile.

Non-precision approaches, while less accurate, are easier to fly because the altitudes are mostly level flight with only one needle to follow. On reaching the minimum descent altitude you should have established a personal visual descent point from which a normal straight-in landing can be accomplished. Other wise do not descend below the circling minimums.

Localizer types of non-precision approaches are the localizer, LDA and SDA. Other non precision approaches are the VOR, and the Airport surveillance radar approach (ASR). ASR approaches require a published plate. A given approach may be entered as (1)a straight in approach or (2) as a full approach.

--Once on the approach use power for descent, level and climb
--Work load must not interfere with control.
--Focus only on the turn when turning.
--Consider downwind landing instead of circling.
--Make small power changes even to climb.
--Never bust minimum altitudes.

Descent from the FAF to the MDA have traditionally been of the 'chop and drop' type but today the use of DME makes stabilized descents more common. The VDP (visual descent point) either created or charted makes it possible for the pilot to prepare for a landing for straight in approaches.

Approach Minimums for Non-precision
--Straight in minimums are visibility only.
` --Circling minimums require a ceiling.
--Get down to the MDA well before the airport.
--You win by being allowed to make a scud run to the airport.
--Nonprecison approaches should be flown precisely.
--Level off at the MDA and let person not flying look for airport.

Complex Approach Minimums
Lowest minimums only if:
1. Local altimeter setting
2. Identify 2.5 DME fix
3. Straight in landing

Stepping Up to the Step-Down Approach
The step-down is used to give the non-precision approach lower minimum descent altitudes. The basic non-precision without the step down takes you to the MDA right after the FAF. The step-down requires that you make one or more altitude stops before reaching the MDA. The steps are based upon aircraft category and the altitudes are critical with minimal obstacle clearances.

There are two methods of doing the approach. One is to follow the published procedure and chop-and- drop between each step while maintaining a constant ground speed in the drop and level flight. The other option is to calculate the rate of descent for the entire procedure and initiate that rate of descent at a constant ground speed throughout. The latter procedure will allow you to cross each fix at the proper altitude in a stabilized airspeed approach. 

A Lesson
In level flight establish aircraft in your approach configuration. Note (record) for memorization the configuration settings of gear, flaps, and power for level flight. Index these settings as what you will use for each time you level off. If you are not loaded according to your standard practice, you should give your descent and level off procedure a trial run before making the approach.

The step-down descent requires superior aircraft control. Descent is commenced first with carburetor heat and a power reduction, rudder, and then elevator. Touches of rudder are best with power changes, left for reductions and right for increases.

The 3 to 1 descent glide plane can be determined quickly by dividing the altitude to be lost by three and using the dividend to give you the miles required to make the descent. A 3 to 1 descent will require 6 miles to descend 1800', 5 miles for 1500' and so on. To find the required vertical speed for the 3 to 1 profile multiply your ground speed by five and add 50. Ground speed of 90 x 5 = 450 + 50 = 500 or 500 feet per minute descent will keep you on the descent profile. at 120 knots you will need 650 fpm descent. Descents over 500 fpm are uncomfortable for passengers.

Title of a step-down approach reveals the approach gradient. A letter instead of a runway number tells you that the descent requires more than 400 fpm descent. This also tells you that only circling minimums apply. A straight-in can be made if conditions allow a normal approach and landing. The step fixes will be on the GPS data base if they have a five letter identifier. Fixes shown by triangles are not in the database and are titled as a CF (centerline fix) for a runway number.

With consummate skill, a pilot could determine both the speed and descent rate required to make a constant descent from fix to fix to fix. Never dive for the MDA. You may need to descend in excess of the slope that gets you to the MDA at the exact time for the missed. Otherwise, you can have no expectation of making a normal approach to landing. This eliminates leveling off and you should reach a visual descent point and MDA at the same time. Not easy but certainly something to strive for. A MAP at the threshold of a mile long runway and a MDA below 400' AGL will put you at the far end of the runway unless your slope exceeds the 3 to l norm.

 

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