Lost Communications (The Mumble)

The pilot diagnoses a silent radio before declaring it dead. The AIM's radio technique paragraph puts the check first: "Be alert to the sounds or the lack of sounds in your receiver. Check your volume, recheck your frequency, and make sure that your microphone is not stuck in the transmit position" 1. The pilot checks these items in the Warrior, in this order:

• volume up and squelch open on the radio in use
• the frequency read back from the display against the chart
• the correct radio selected on the audio panel for transmit and for receive
• the audio panel switches, speaker and headset, in the right places
• the headset plugs seated, both of them
• the hand microphone as a backup for the headset's microphone.

Most radios that go silent have not failed. The frequency is wrong by one digit. The transmit selector is on the other radio. The pilot turned a volume knob down while a passenger talked. A headset plug came half out on a bump. Each of these faults produces silence.

The checklist fixes each of these faults in ten seconds. A pilot who declares the radio dead without the checklist skips a ten-second fix. The radio stays silent.

The stuck microphone

A stuck microphone blocks the frequency for everyone on it. The AIM says: "Frequency blockage can, and has, occurred for extended periods of time due to unintentional transmitter operation. This type of interference is commonly referred to as a 'stuck mike'" 1. The frequency goes quiet after the pilot's own call, because the open transmitter blocks each other call. The pilot's first check is the push-to-talk switch, released and pressed again. The AIM's first rule of radio technique is "Listen before you transmit," and "if you have just changed frequencies, pause, listen, and make sure the frequency is clear" 1.

A radio has two halves, a receiver and a transmitter, and either can fail alone. The receiver can fail with the transmitter working. The transmitter can fail with the receiver working. Both can fail. The AIM's paragraph on tower communications with a failed radio gives a procedure for each case.

Receiver dead, transmitter working

The pilot who can talk and cannot hear transmits in the blind. The AIM says: "If you have reason to believe your receiver is inoperative, remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, advise the tower of your type aircraft, position, altitude, intention to land, and request that you be controlled with light signals." The AIM continues: "when you are approximately 3 to 5 miles from the airport, advise the tower of your position and join the airport traffic pattern. From this point on, watch the tower for light signals. Thereafter, if a complete pattern is made, transmit your position downwind and/or turning base leg" 2. The module's call begins with the words "transmitting in the blind." The call gives the position and the intention. The tower answers with a light signal.

Transmitter dead, receiver working

The pilot who can hear and cannot talk answers with the wings or the lights. The AIM says: "Remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, join the airport traffic pattern. Monitor the primary local control frequency as depicted on Sectional Charts for landing or traffic information, and look for a light signal which may be addressed to your aircraft. During hours of daylight, acknowledge tower transmissions or light signals by rocking your wings. At night, acknowledge by blinking the landing or navigation lights" 3. The tower can talk to the airplane by voice, because the receiver works, and the pilot answers with a wing rock. The pilot complies with light gun signals as with spoken instructions.

Both dead

With both halves dead, the procedure is the same, without the listening: "Remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, join the airport traffic pattern and maintain visual contact with the tower to receive light signals" 3. The pilot uses the transponder in place of the radio. The AIM says: "If an aircraft with a coded radar beacon transponder experiences a loss of two-way radio capability, the pilot should adjust the transponder to reply on Mode A/3, Code 7600" 4. A radar controller who sees 7600 knows the airplane has lost two-way radio.

A lost radio is not, by itself, an emergency

A lost radio under VFR is not, by itself, an emergency. The AIM says: "Whether two-way communications failure constitutes an emergency depends on the circumstances, and in any event, it is a determination made by the pilot." The AIM adds: "pilots are expected to exercise good judgment in whatever action they elect to take" 5. The airplane flies without the radio. The pilot flies the airplane, stays VFR, and works the arrival plan.

The AIM's rule for a radio failure in VFR conditions is to "continue the flight under VFR and land as soon as practicable," and the AIM adds that "practicable" is not "possible". A pilot is "not required to land at an unauthorized airport, at an airport unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination" 6.

The flight of N52502

On November 27, 1998, at noon, a Cessna 172 landed on top of another Cessna 172 on runway 23 at Brainerd, Minnesota. The pilot of the airplane on top, N52502, was a 41-year-old private pilot with 1,600 hours, 900 of them in the type. He carried one passenger. A student pilot on a solo cross-country flew the airplane underneath, N80357, and had just touched down. Three people had minor injuries. The weather was clear with 10 miles of visibility 7.

The pilot of N52502 was over a lake north of the airport, sightseeing, when he decided to land. He told the NTSB "that he had made a call on BRD's common traffic advisory frequency (CTAF) of 122.7 and did not hear any other traffic in the area. He then selected the automated surface observing system (ASOS) frequency, obtained the BRD weather and then reselected the BRD CTAF." He "did not see any other traffic while making his straight-in approach to runway 23" 7.

The frequency he used was not 122.7. A mechanic inspected the radios after the accident and found "that the communication radios of N52502 were set to a frequency 135.8 MHz and 122.9 MHz." The report adds, "The CTAF for BRD was 122.7 MHz." Both radios in the student's airplane were on 122.7 7.

The frequency the pilot never heard was busy. The student's written statement says that ten miles out an airliner called on the CTAF and "there were several responses," including two airplanes in the pattern. The student reported the 45 entry at four miles. He reported downwind behind another Cessna. He "reported each leg (downwind, base, final) on the CTAF 122.7."

Before touchdown the student checked that the airplane ahead was clear of the runway and checked his glidepath on the VASI. "There was no transmission by other traffic that would lead me to believe anyone was on base or a long straight final." As he touched down he "heard what appeared to be the sound of metal dragging on the runway," and the airplane rose on its right side and rolled left 7. A witness saw N52502 overtake the student's airplane and land on it.

The probable cause was "the visual lookout not obtained/maintained by the pilot. Contributing factors were the unicom frequency not selected and the traffic advisory not issued by the pilot" 7.

Where the accident could have been prevented

No radio was broken. The accident was three decisions. Each decision is listed below with its PAVE category and the action that would have prevented the collision.

The regulation allows a VFR airplane with a dead radio to land at a towered airport on three conditions. Section 91.129(d) says: "If the aircraft radio fails in flight under VFR, the pilot in command may operate that aircraft and land if— (i) Weather conditions are at or above basic VFR weather minimums; (ii) Visual contact with the tower is maintained; and (iii) A clearance to land is received" 8. The clearance to land, with the radio dead, is the steady green light. Section 91.126(d) says the same for a tower airport in Class G 9.

The technique

The AIM gives the arrival: "Remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, join the airport traffic pattern and maintain visual contact with the tower to receive light signals" 3. The steps, in order, are:

• squawk 7600
• stay clear, above the Class D or outside it
• watch the pattern until you can see the runway in use and the flow
• enter the pattern conforming to the flow, on the 45
• watch the tower for the light gun on downwind and again on final
• rock the wings by day, or blink the lights by night, for each signal received.

Steady green in flight is cleared to land. Flashing green is return for landing, and the steady green light follows. Steady red is give way and keep circling. Flashing red is airport unsafe, do not land 10. The pilot who can transmit reports position and intention on the tower frequency, in the blind, at each leg.

No green, no landing

A landing at a towered airport without the green light is a landing without a clearance. The regulation's third condition is that "a clearance to land is received" 8. Flashing red on final means go around. No light on final means go around and fly the pattern again so the tower can see the airplane. The AIM gives the same rule for a departure with a dead radio: after leaving the ramp, "watch the tower for light signals or monitor tower frequency" 11. The pilot does not take the runway, for landing or for takeoff, until the tower clears it with a light signal.

At a non-towered airport there is no light gun and no clearance. The pilot with the dead radio flies the standard pattern, at pattern altitude, on the 45, and watches for traffic more than usual. The other pilots self-announce around an airplane they cannot hear. AC 90-66C says: "procedures at airports without operating control towers generally do not require the use of two-way radios; therefore, pilots should be especially vigilant for other aircraft while operating in the traffic pattern. Pilots of inbound aircraft that are not capable of radio communications should determine the runway in use prior to entering the traffic pattern by observing the landing direction indicator, the wind indicator, landing and departing traffic" 12. The pilot with a working transmitter and a dead receiver still makes each call. The pilot with neither flies the pattern the other pilots expect.

When the radio died with the electrical system

A radio that fails as the panel lights dim and the ammeter shows discharge is not a radio problem. The electrical system failed, and the radio was the first sign the pilot noticed. The Warrior's manual gives the response: "Reduce electrical load. Alternator Circuit Breakers - Check. 'Alt' Switch - Off (for 1 second), then On. If the ammeter continues to indicate no output, or alternator will not stay reset, turn off 'Alt' switch, maintain minimum electrical load, and land as soon as practical. All electrical power is being supplied by the battery" 13.

The pilot sheds load and plans for the battery's remaining minutes. A landing comes before troubleshooting. If the battery has power left, the pilot turns the transponder and the radio back on for the pattern. The pilot still flies the light gun arrival as if both were dead.

The telephone

A mobile phone is a useful backup. The AIM includes the telephone in the procedure for a radio that fails on the ramp: "call the tower by telephone and request authorization to depart without two-way radio communications" 11. The tower's number is in the Chart Supplement. After a NORDO landing the pilot calls the tower before taxiing anywhere the tower has not cleared. In flight, the pilot calls only when the workload allows, which in a Warrior with one pilot means straight and level, clear of the pattern. The pilot never calls on final.

Section 91.185 is a rule for another rating. Its title is "IFR operations: Two-way radio communications failure," and its first sentence applies it to "each pilot who has two-way radio communications failure when operating under IFR" 14. Its route and altitude rules are for a pilot in cloud on a clearance. A VFR pilot has one rule. It is the same rule the IFR section gives for VFR conditions: "continue the flight under VFR and land as soon as practicable" 14. A VFR pilot who flies a remembered IFR procedure follows a clearance that no one gave.

The habits

A pilot prevents a silent radio more often than the pilot handles one. Before each flight:

• a radio check before taxi, with the ground controller or on the CTAF
• both radios tuned when the airplane has two, one to the frequency in use and one to the next
• the frequencies for the route set in advance, from the chart and the Chart Supplement
• the light gun table recited from memory before each solo to a tower field.

The AIM's departure paragraph gives the last habit. A pilot who finds the radio dead before leaving the ramp fixes it or telephones the tower. The airplane does not taxi in silence 11. A pilot who runs the silent-radio checklist on the ground has practiced it before a failure in flight.