ASRS Directline

 Issue Number 6 : August 1993

Lost Communication

by Charles Drew, Andrew Scott, and Robert Matchette

The key to any good relationship, whether in marriage, at the office, or between pilot and controller is communication. Pilots and air traffic controllers know that the safe and efficient movement of air traffic requires good voice communication between air traffic control facilities and aircraft, yet most pilots and controllers have experienced a loss of communication at least one time or another, for a variety of reasons.

A Near Thing

The following event, reported to ASRS by several participants, illustrates the problems that can arise when communication is not possible. A Center facility had jurisdiction over two air carrier aircraft, both at flight level 350 and on a nearly head-on converging course. The Captain of air carrier X writes:

The First Officer of air carrier X adds:

And a Controller provides the conclusion:

Several communications-related problems occurred here, including the flight crew of air carrier Y not maintaining a listening watch on frequency, and aircraft X being sent to the wrong frequency by ATC--perhaps with insufficient time for a recovery. How many ways can you lose your com (and your calm). Well...

There Must Be 50 Ways...

There must be at least fifty ways to lose communication and here are just a few:

  • misset the aircraft audio panel
  • set the aircraft radio volume too low
  • assign an incorrect frequency to an aircraft
  • experience an electrical system failure
  • forget to turn on the aircraft alternator
  • have a "stuck mike"
  • tune the wrong frequency on the aircraft radio
  • have an ATC facility radio failure
  • get frequency blockage due to radio congestion
  • fall asleep
  • forget to switch to a new frequency
  • try to communicate on the wrong radio.
  • Sound familiar? Perhaps you can think of thirty-eight more. Given the potential hazards, a review of the causes and effects of interruptions to communication sounds like a pretty good idea. An initial investigation, using ASRS records, examined the causes and effects of loss of communication events. A follow-up study looked at the principal human-factors issues involved in delayed recognition of loss of communication on the part of pilots who experienced this problem. Here are the six most interesting findings of these two studies:

    Causes for Communication Interruption

    Misset Radios

    As can be seen in Figure 1 below, pilots' inadvertent missetting of aircraft radios or audio selectors accounted for over half of all interruptions to communication. Notes a pilot:

    Figure 1 Causes of Loss of Communications

    Radio Problems

    An aircraft radio problem or failure was the next most commonly noted cause for loss of communication, but pilots of general aviation (GA) aircraft (specifically light single-engine types) were more likely to experience loss of communication through aircraft radio failure than were operators of other aircraft types. The following report from a general aviation pilot illustrates not only the potential problems with general aviation aircraft electrical systems, but also a reasoned response by the reporter, and the invaluable employment of a hand-held portable transceiver:

    Blocked Frequency

    A "stuck mike" (in which a microphone, radio transmitter, or audio selector panel failed in the transmit mode) was known to be the cause in about 60 percent of blocked frequency incidents. ATC facility transmitters and combined weather conditions/frequency overlap each accounted for less than 10 percent of occurrences. The following report is typical of stuck mike incidents:

    And in another classic stuck mike event:

    And later, when asked to contact the Facility Supervisor on the telephone:

    "He [the Supervisor] said 'Now how are your blank-blank radios doing?...We have everything on tape, everything! We had to go to a backup frequency because of your language. You apparently had a hot mike.' " (ACN 153914)

    Duration of Lost Com

    Figure 2 shows the average (mean) duration of the loss of communication, which ranged from a low of 30 seconds to a high of 1 hour. When various causes for loss of communication were combined, the average duration was 7.6 minutes.

    Figure 2 Communications Interuptions

    Phase of Flight

    In what phase of flight are pilots most likely to experience a loss of communication? The answer differs depending on whether the operator is an air carrier or general aviation. (See Figure 3.)

    Figure 3 Flight Phase and Type of Operation

    Air Carrier = Cruise

    According to the McDonnell Douglas 1992 Commercial Jet Transport Safety Statistics review, air carrier aircraft spend an average of 64 percent of total flight time in cruise, thus it is not surprising that air carrier pilots experience the majority of event occurrences in the cruise phase, but we found that there may be additional factors. On long distance routes, and while in cruise, it is generally accepted that air carrier flight crews will experience lowered levels of attention due to reduced stimulation from cockpit management duties, which may lead to a reduction in pilot monitoring of radio traffic. From an air carrier pilot:

    GA = Approach and Landing

    Combined approach and landing phases provided the greatest number of events for pilots of light single and twin GA aircraft. Why? Well, for one thing GA pilots, when all types of operations are considered, probably spend less time in cruise than do air carrier flight crew. For another, they usually have significantly less cockpit automation and often a single-pilot operation, therefore a general aviation pilot may be required to devote greater attention to positional and situational awareness while in cruise, which may result in heightened levels of awareness. However, a general aviation pilot on an instrument approach and landing usually has fewer and less sophisticated system and navigational devices, less total and recent experience, and less opportunity for task sharing when operating single-pilot. He or she often has to cope with a higher individual workload than their airline counterpart, and the opportunity for task overload is enhanced. Of course, sometimes a pilot makes his or her own problems, as in the following report by a flight instructor:

    And after the reporter had spent some time in the now quiet environment...

    "What's wrong? No speaker! Darn. Switch on! ...Tower called...'Where have you been? We've been calling you for the last five minutes.' " (ACN 157097)

    Low Experience = More Loss of Com Events

    There is a significantly increased opportunity for lost com occurrences when one or more of the flight crew is low time on the aircraft type--this is particularly true for general aviation pilots. Figure 4 provides the frequency of lost communication events vs. time-in-type for GA pilots. (A similar, but less pronounced pattern was revealed for air carrier pilots.)

    Figure 4 GA Pilot Time in Type vs. Event Frequency

    Times in Figure 4 are in 50 hour segments from 1 hour to 50, 51 to 100, and so on. The "spike" noted in the 251 to 300 hour segment is probably a result of "rounding" by reporters. (A reporter with 276 hours, or 310 hours for example, may tend to round his experience to 300 hours.)

    Delay in Recognition

    Preoccupation or distraction with tasks in high workload situations was commonly noted in delayed recognition of loss of communication. Note the following report:

    At the opposite end of the causal spectrum, loss of awareness or lowered levels of awareness was also a significant contributor to delayed recognition of com loss:

    Recognition of Com Loss

    Most commonly, flight crew discover their communication loss when they made a normal attempt to communicate with ATC:

    The next most common reason for communications recovery was intervention by the controlling facility on another frequency, or through company or ARINC channels as illustrated in the following report:

    Observations and Recommendations

    Let's see if there may be some useful recommendations for reducing the frequency, duration and severity in lost communication events.

    General ConsiderationsMan on Telephone

    As noted, the most common reason for a misset radio is inadvertent pilot mis-selection of a frequency. The best solution to this problem is the old solution--proper attention to detail and good cockpit management and monitoring on the part of the flight crew.

    1. Pilots should be aware that there is a significantly increased opportunity for a lost communication event when pilot experience in the aircraft type is low. Continued emphasis on the value of situational awareness will help.

    2. Pilots often experienced difficulty in returning to an original frequency if there was an error in selection or clearance to a new frequency. A simple and effective aid for pilots is to write down assigned frequencies; should a loss of communication occur at the point of a frequency change, the pilot may easily return to the previous frequency.

    3. One reporter, as a final thought in his misset frequency report, suggested that facility frequencies be reproduced on enroute navigation charts. This could be either the primary sector frequencies, or perhaps a "general" frequency shared by a number of sectors within a facility through which a recovery could be effected.

    4. The seriousness of "stuck mike" events could be significantly reduced by the use of transmitter "time-out" devices that terminate transmission after a reasonable time period.

    5. Military aircraft, in addition to their normal radio package, are usually fitted with radios that receive on "Guard" frequencies 121.5 and 243 MHz. The volume of these emergency radios cannot be reduced, and in-coming transmissions on this radio will override other communications. If all aircraft operating in the ATC system were fitted with such radios, recovery of aircraft with misset radio and blocked frequency problems could be effected more readily.

    GA Pilots

    1. Loss of situational awareness in high workload situations, and problems with aircraft radios or electrical systems were commonly noted problems for GA pilots. Thorough pre-flight planning can help reduce the impact in high workload situations. GA pilots should know their electrical system, and should constantly monitor the electrical system in flight and should consider terminating the flight at the first signs of system problems.

    2. Where high cockpit workloads contribute to loss of communication such as during Approach and Landing, adherence to cockpit disciplines (such as the sterile cockpit), and maintenance of positional awareness should serve to reduce delays in event recognition.

    3. A number of ASRS reports from general aviation operators note the use of hand-held portable aviation radio transceivers--as backup to aircraft mounted radio equipment. In four incidents the "hand-held" can be credited with a communications "save," and there are additional reports among those reviewed for this study that cite effective use of these portable communications radios.

    Transport Pilots

    1. Review of pertinent records indicates that pilot recognition of interrupted communication in the Cruise phase, (notable for a low workload environment and a point where ATC communication and chatter are minimal), may be facilitated by the motherhood and apple pie solution of constant situational and positional awareness.

    2. For high altitude flight, noting the location of ARTCC Facility boundaries as marked on charts should serve to alert pilots to required hand-offs.


    1. Controller intervention through use of company or ARINC frequencies is effective when used.

    2. Those incidents wherein an ATC facility used an alternate communications process to "recover" an interrupted-communication aircraft showed good success. Use by facilities of alternate communications procedures such as company frequency, aircraft relays, SELCAL, ARINC, and ACARS tends to be effective.

    3. It is suggested that ATC facilities review alternate communications possibilities in the event of frequency blockages, including periodic resting of the battery-operated Gonset radios.

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