Flying the Vertical Component of a
Non-Precision Approach
By Hugh Davis
Every flight, whether a trip around the traffic pattern or a space shuttle mission, has both a lateral and a vertical component. Data has shown that we have a pretty good idea of how to fly the lateral component. However, the data also indicates that to increase situational awareness, we must also concentrate more on the vertical component.
The AOPA Air Safety Foundation’s Joseph T. Nall Report for 2009 shows that accidents or incidents caused by pilot error improved 10 percent over the 2008 figure. However, 75 percent of all accidents were attributed to pilot error, with 19 percent of the accidents identified as fatal in the descent and approach phase of the flight. Weather, descent, and approach segments made up 50 percent of the accidents. In addition, 40 percent of the accidents occurred in the landing phase but were nonfatal. Even though business and corporate flying has a better record then that of the other segments of general aviation, its accident rate increased by 10 percent, according to the report.
ACCIDENT RECAP
Some general aviation accidents that occurred during the descent, approach, and landing phase are:
- November 22, 2004, a Gulfstream III approaching Houston Hobby’s Runway 4 in foggy conditions crashes on the centerline but short of the runway. A contributing cause to the accident is an unstable approach.
- October 19 2005, a Hawker 700 crashes due to an unstablized landing. The tower offered a new runway clearance that would allow a shorter taxi distance to the FBO.
- October 24, 2004, a Beech King Air 200 crashes after a go-around in IMC conditions beyond the approach path of the Martinsville, Virginia, airport. The probable cause is loss of situational awareness during the approach and go-around.
Some noteworthy air carrier accidents involving the same scenario include:
- American Airlines Flight 1420 at Little Rock, Arkansas, attempted an approach and landing during thunderstorm activity.
- Korean Airlines Fight 801 approaching Guam at night was cleared for an ILS approach with the glide slope out of service.
Remember, every flight consists of lateral and vertical components. The first instrument landing system to give both lateral and glide path information was designed in 1929, first used by a commercial airliner in 1938, and then in 1941 approved for installation at six airports around the country. The ILS system has changed little since then.
In 2007, WAAS was introduced to aviation, providing a satellite-based precision approach to many general aviation airports in the United States that previously had none.
ON OUR OWN
Unbelievably, for many years pilots have been on their own to compute the vertical path of a non-precision approach from the final fix to the touchdown point. According to the accident reports, we have not been doing that well. Hopefully, with the increase in the number of WAAS approaches available to general aviation airports we will see a reduction in the accident rate. Even with these technological changes, it will still be important to maintain situational awareness on the vertical path.
The non-precision approach method that has been taught and practiced for years is to depart the final approach fix at something other than a stabilized descent rate, then level off at the MDA and wait to see the runway. If you don’t see it, make a missed approach based on DME or time. Imagine on a visual approach switching over to the tower seven miles out from the runway and receiving clearance to land. At that point you immediately drop down to 400 feet above the ground and level out until over the runway, then make the landing. If we wouldn’t do this in VFR, why would we do it in IFR conditions?
CONSTANT RATE
Now think about another scenario involving a constant-rate-of-descent approach. The flight is cleared for the approach. Coming up on the final approach fix, the gear and flaps are extended and airspeed is stable. The landing check is complete. The power is reduced for a smooth constant-rate descent to the MDA while at the same time checking the vertical profile—for every mile from the runway your aircraft should be 300 feet above the touchdown zone (i.e., when 3 miles from the runway you should be 900 feet above the touchdown zone elevation).
When the runway is visible the constant-rate-of-descent approach can be continued to landing. If the runway is not in sight when approaching the MDA, a go-around is the only safe course of action. This procedure has been adopted by many flight departments including air carrier training programs, and endorsed in the newly released FAA Instrument Training Handbook.
However, several essential elements have to occur prior to the reaching the final approach fix. After receiving the weather information and runway assignment, the pilot or crew should Build the Approach into the FMC or GPS navigator. The next step would be to set the appropriate airspeed and altimeter Bugs. Finally, Brief the approach and missed approach procedures. Build It, Bug It, Brief It
Now you arrive at the final approach fix with gear down, flaps set, and the landing checklist complete. This is a lot less stressful than trying to complete a multitude of tasks at and inside the final approach fix. The later almost always results in an unstable approach.
FIGURING DESCENT RATE
A technique to use for the constant-rate-of-descent approach is to have the autopilot engaged and at the final approach fix select indicated airspeed or vertical speed mode. Multiply the groundspeed by 5 for a constant rate of descent based on a 3-degree glide slope. For a little higher angle of descent increase the rate of descent and likewise reduce the vertical speed for a slightly less-than-3-degree angle of decent.
Always monitor your altitude. At 4 miles out from the runway you should be 1200 feet above touchdown, 900 feet at 3 miles, and so on. If your minimums are 450 above the touchdown zone, your visual descent point or go-around point is 1½ miles from the runway. Remember, visual descent point or go-around point is height above touchdown zone elevation divided by 300. It might be helpful to write down the required altitude at each mile from the runway.
In conclusion, building the approach in the FMC or GPS, and practicing the technique during all of your approaches to landing will greatly increase your situational awareness during the real IFR approach and landing.
Hugh Davis is a former FlightSafety International Commander instructor. He flies a 690B for an owner.
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