Fixed Card NDB/ADF Approaches
Good evening aviation enthusiasts! I hope everybody’s memorial day weekend is beyond great. Today I will be explaining how a non-precision NDB ( Non-directional beacon ) instrument approach is performed and a few tricks I learned through my recent instrument flights. NDB approaches require an aircraft to be equipped with an ADF ( Automatic Direction Finder ) radio to tune to the station that is near an airport. These non-precision approaches are becoming quite outdated as more modern avionics are becoming readily available. Unfortunately, if an aircraft is equipped with an ADF radio, NDB approaches with holding is fair game on the instrument checkride. ADF is actually quite a fascinating piece of equipment due to the frequencies that can be acquired including some local AM radio stations!
Step-by-step I will explain how I personally brief the approach plate and perform tracking, going missed on the approach and holding over the station. Of course, everybody performs things differently in aviation. I have developed my own preferred method towards operating the navigational instrument. I think that the way I was taught really allowed me to visualize the basic math that was involved. My personal choice when shooting these approaches is by not rotating the ADF compass, which is also considered leaving it “fixed card.“ (**Fixed Card refers to leaving the compass stationary with North remaining up regardless of the aircraft’s position**)
The examples being used are taken from the FAA Testing Supplement (Figure 127 – NDB RWY 28 at Lancaster/Fairfield County Airport [I15]
Prepare – After starting up the airplane and running through the checklist, the first thing I do is place my approach plate in a position that can be easily referenced at a moment’s glance. I then start at the top of the plate and input the ADF freq. (In this example, I would tune 338, which is located 5.3 nm from the field) I would then put the Columbus ASOS weather frequency in my COM2 radio (**Columbus WX station is used since the Lancaster field doesn’t have a station and as stated by the approach plate, Columbus/Rickenbacker altimeter setting should be used**) Finally, I would perform my run-up and after swapping to tower, tune the CTAF for Lancaster/Fairfield in the COM1 standby. Brief the approach plate and understand the information required to perform the approach such as: Final approach course, Initial Approach Fixes (IAF’s), Missed Approach Instructions and MAP ( Missed Approach Point ), Holding pattern entry type (Direct, Parallel, Teardrop), and most importantly the step-down altitudes and descent minimums for the appropriate airspeed based on type of aircraft being flown.
Small Corrections – After taking off and departing the airspace, turn in an initial direction to the NDB station so that that ADF needle faces north. (The easiest way to understand where the aircraft is in comparison to the station is by taking the arrow on the ADF instrument and cross-referencing it with the heading indicator. Whatever heading the opposing end of the arrow is facing is the current location of the aircraft in relation to the station. (The needle will ALWAYS point towards the station) Once established on a direct course towards the NDB station, corrections can be made by understanding the amount of deflection that occurs on the ADF compass. The easiest way I can explain this is that if say the needle starts to deflect 20 degrees left on the ADF, correct this by turning 40 degrees left on the present heading and hold this until the needle on the ADF also turns 40 degrees left, then proceed by turning back to the original heading. (**Note that if any wind correction is needed, turn 10 to 20 degrees in the direction needed so that the ADF needle will stay centered up and down pointing directly towards the station without deflecting after a few minutes of tracking the station**)
Prepare and Execute – As soon as practical, attempt to identify the station just as you would a VOR or Localizer NAV frequency and verify that it is working/correct. To figure out your distance from the station, tune the ADF frequency into the DME (Distance Measuring Equipment). In this example, we use the DME to figure out where our MAP is established and at what point we should begin to descend down to minimums. Always advise intentions on the traffic advisory frequency and allocate proper separation from other aircraft operating within the airspace you are entering. (We would transmit our intentions on 122.8, the CTAF for Lancaster County Airport) As the DME shows that you are approaching the station (Anywhere around 2-5 nm away) the needle on the ADF may begin to deflect in which very slight corrections must be made to ensure that you don’t orbit the station. (**Chasing the ADF needle is BAD and results in confusion when in the vicinity of the NDB station.**)
Passage – After arriving at the station, the needle on the ADF compass will deflect and fall 90 degrees either left or right depending on which side you passed the station. The aircraft should then be turned to the outbound course heading where the procedure turn can be initiated. Have the timer ready and zeroed out so that once the DME shows around 4-5 nm away from the station you can turn and make the course reversal. (In this example, after reaching the station, we would turn right to a heading of 067 where we start our time and after one minute, we will begin to make a standard-rate turn to the right ending on the final approach course of 277 where the ADF needle should be centered north without any deflection pointing towards the station.) Once again, any deflection and wind correction should be made as soon as possible without over-correcting and getting further off course.
Memorize the Procedure – Looking at the step downs for the specified approach at Lancaster, we know that once we pass-over the station, we can descend from 2,700 feet down to our minimums of 1,620 feet (800 feet above the field with a minimum of 1 mile visibility). Descend at a acceptable rate given the distance to the MAP (Missed Approach Point, which is 5.3 nm from the station). Like any other approach, after arriving at the MAP, immediately start a climb and perform the missed approach procedures as published. (**In this example, we would make a climbing left turn up to 2,700 feet and fly direct to LOM [NDB station] where we will perform a teardrop entry and intercept the 097 outbound course of the holding pattern and fly that heading for one minute.**) We will then proceed to make a 180 degree turn to the inbound course of 277 where the ADF needle should indicate centered without any deflection and again time each inbound and outbound course for one minute. Timing corrections should be made depending on present winds aloft.
NDB/ADF approaches can seem difficult and rather confusing at times, but they are actually very basic and a simple way to navigate when weather conditions are decreasing. Like I mentioned earlier, everybody learns things differently and using a fixed-card ADF compass might not work as visualizing the station direction by rotating the compass may help. I certainly don’t expect student pilots and individuals just starting their instrument training to understand this blog post, but once a basic understanding of how these non-precision approaches work, I can almost guarantee that my method will hopefully benefit in some way or another.
I appreciate any feedback and suggestions for future blogs. Please like, share and comment with any questions regarding aviation related material and I will reply as soon as I possibly can! Thank you very much for reading and expect more blogs to come in the future (Maybe less technical?). As always, safe flying for all and enjoy each and every moment spent in the sky. To most people, the sky is the limit, but for pilots, the sky is where we belong.
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