These few words mean so much and are so misunderstood. When Air Traffic Control utters these words while a pilot is conducting an instrument approach to an uncontrolled airport or one where the tower is closed what it means is that it's okay for the pilot to change to the airport advisory frequency to announce his intentions to land and to caution other aircraft that might be in the traffic pattern or waiting to take off that an aircraft is on the instrument approach.
The idea behind this phrase is great. In this fashion other aircraft that might be operating under visual flight rules (VFR) should be on the lookout for an aircraft emerging from the clouds on final and give way. They might also announce their presence on the frequency so the pilot on the instrument approach will be aware of their presence and look carefully to avoid them when and if he breaks out of the clouds during the approach.
Therein lies the rub. It is possible that the pilot on the approach will fly his aircraft to minimums, like 200 feet above the ground before he looks out to see the runway environment. At that point it's too late to see and avoid the other aircraft and the hazard of a collision with an airplane operating under technically legal VFR is possible.
But that isn't the only risk and this one is the worst. Often when the controller approves a change to advisory frequency, all too often the pilot switches his primary radio to the advisory frequency without tuning in approach control on the second radio and turning up the volume so he can listen on both radios. Why does this happen so often? Because the pilot is concerned that he won't be able to hear aircraft on the advisory frequency responding to his call in the blind or that he will not hear their calls in the blind confused instead by the chatter on the approach control frequency.
What some pilots don't understand is that approach control radars have a low altitude alerting feature that is customized to instrument approaches at that airport. In short, it flashes the data block and sounds an aural alarm to the controller should the aircraft on the approach deviate from the establish approach parameters of safety. This occurs even after the frequency change and until the instrument flight plan is closed. The controller is then obligated to give a low altitude alert that goes something like: "November (AIRCRAFT NUMBER) low altitude alert, check your altitude immediately!" Now this is one great safety feature because if the pilot is concentrating on the approach and perhaps misses an "off" flag on his instruments, follows a false glideslope, has a sticking or lagging altimeter, or just loses his concentration, that nagging controllers' voice can be a wake-up call that saves lives. If given timely, the proper response is to check ones' descent, execute a missed approach if necessary and sort things out instead of crashing into the terrain below.
The pilot can't do this if he has either failed to insert approach control's frequency in his second radio or doesn't have the volume up loud enough to hear the alert. This simple oversight has prevented the avoidance of many accidents.
When on an instrument approach lots of stuff is going on. With the advent of GPS, WAAS and who knows what next, the pilot workload has been increased not decreased. This alert feature which has been around for years and ignored too often by controllers and missed by pilots can make a huge difference. In most accidents we have investigated, the controller gives the low altitude alert and only talks to himself because the frequency has already been changed in the primary radio by the pilot. Sometimes the alert is given too late because controllers ignore them due to too many false alerts. The result is often a crash. Everyone makes mistakes so tuning the other radio to approach while monitoring the advisory frequency can save your life. DO IT !!!!!
Arthur Alan Wolk
Note: The term VFR means the operation of an aircraft under "visual flight rules" ie. the FAR's. Some time ago the FAA began to use the acronym VMC, "visual flight conditions" to describe what we pilots knew for an eternity as VFR. Those of us pilots old enough know that VMC is the FAA's acronym for "velocity minimum control" and has to do with the velocity below which a twin engine aircraft will no longer maintain directional control if the critical engine fails on takeoff. The constant changing of well known acronyms by the FAA brings to mind one that most pilots would like to have implemented with regard to the FAA's continued existence. Its known as DOA.