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Flight Operations in Volcanic Ash

Introduction:

  • Severe volcanic eruptions which send ash into the upper atmosphere occur somewhere around the world several times each year
  • Flying into a volcanic ash cloud can be exceedingly dangerous
  • Piston-powered aircraft are less likely to lose power but severe damage is almost certain to ensue after an encounter with a volcanic ash cloud which is only a few hours old

  • The ash plume may not be visible, especially in instrument conditions or at night; and even if visible, it is difficult to distinguish visually between an ash cloud and an ordinary weather cloud
  • Volcanic ash clouds are not displayed on airborne or ATC radar
  • The pilot must rely on reports from air traffic controllers and other pilots to determine the location of the ash cloud and use that information to remain well clear of the area
    • Additionally, the presence of a sulphur-like odor throughout the cabin may indicate the presence of SO2 emitted by volcanic activity, but may or may not indicate the presence of volcanic ash
  • Every attempt should be made to remain on the upwind side of the volcano

  • It is recommended that pilots encountering an ash cloud should immediately reduce thrust to idle (altitude permitting), and reverse course in order to escape from the cloud
  • Ash clouds may extend for hundreds of miles and pilots should not attempt to fly through or climb out of the cloud
European Iceland Volcano
Figure 1: 2010 Iceland Volcano

Indications:

  • Flight crews who have experienced encounters with volcanic dust clouds reported:
    • Smoke or dust appearing in the cockpit
    • An acrid odor similar to electrical smoke
    • Multiple engine malfunctions, such as compressor stalls, increasing EGT, torching from tailpipe, and flame-outs
    • At night, St. Elmo's fire or other static discharges accompanied by a bright orange glow in the engine inlets
    • A fire warning in the forward cargo area

What to do:

  • It may become necessary to shut down and then restart engines to prevent exceeding EGT limits
  • Volcanic ash may block the Pitot system and result in unreliable airspeed indications
  • If you see a volcanic eruption and have not been previously notified of it, you may have been the first person to observe it
    • In this case, immediately contact ATC and alert them to the existence of the eruption
    • If possible, use the Volcanic Activity Reporting (VAR) Form
    • Items 1 through 8 of the VAR should be transmitted immediately
    • The information requested in items 9 through 16 should be passed after landing
    • If a VAR form is not immediately available, relay enough information to identify the position and nature of the volcanic activity
    • Do not become unnecessarily alarmed if there is merely steam or very low-level eruptions of ash
  • When landing at airports where volcanic ash has been deposited on the runway, be aware that even a thin layer of dry ash can be detrimental to braking action. Wet ash on the runway may also reduce effectiveness of braking. It is recommended that reverse thrust be limited to minimum practical to reduce the possibility of reduced visibility and engine ingestion of airborne ash
  • When departing from airports where volcanic ash has been deposited, it is recommended that pilots avoid operating in visible airborne ash. Allow ash to settle before initiating takeoff roll. It is also recommended that flap extension be delayed until initiating the before takeoff checklist and that a rolling takeoff be executed to avoid blowing ash back into the air

Precipitation Static:

  • Precipitation static is caused by aircraft in flight coming in contact with uncharged particles. These particles can be rain, snow, fog, sleet, hail, volcanic ash, dust; any solid or liquid particles. When the aircraft strikes these neutral particles the positive element of the particle is reflected away from the aircraft and the negative particle adheres to the skin of the aircraft. In a very short period of time a substantial negative charge will develop on the skin of the aircraft. If the aircraft is not equipped with static dischargers, or has an ineffective static discharger system, when a sufficient negative voltage level is reached, the aircraft may go into “CORONA.” That is, it will discharge the static electricity from the extremities of the aircraft, such as the wing tips, horizontal stabilizer, vertical stabilizer, antenna, propeller tips, etc. This discharge of static electricity is what you will hear in your headphones and is what we call P-static
  • A review of pilot reports often shows different symptoms with each problem that is encountered. The following list of problems is a summary of many pilot reports from many different aircraft. Each problem was caused by P-static:
    • Complete loss of VHF communications
    • Erroneous magnetic compass readings (30 percent in error)
    • High pitched squeal on audio
    • Motor boat sound on audio
    • Loss of all avionics in clouds
    • VLF navigation system inoperative most of the time
    • Erratic instrument readouts
    • Weak transmissions and poor receptivity of radios
    • "St. Elmo's Fire" on windshield
  • Each of these symptoms is caused by one general problem on the airframe. This problem is the inability of the accumulated charge to flow easily to the wing tips and tail of the airframe, and properly discharge to the airstream
  • Static dischargers work on the principal of creating a relatively easy path for discharging negative charges that develop on the aircraft by using a discharger with fine metal points, carbon coated rods, or carbon wicks rather than wait until a large charge is developed and discharged off the trailing edges of the aircraft that will interfere with avionics equipment. This process offers approximately 50 decibels (dB) static noise reduction which is adequate in most cases to be below the threshold of noise that would cause interference in avionics equipment
  • It is important to remember that precipitation static problems can only be corrected with the proper number of quality static dischargers, properly installed on a properly bonded aircraft. P-static is indeed a problem in the all weather operation of the aircraft, but there are effective ways to combat it. All possible methods of reducing the effects of P-static should be considered so as to provide the best possible performance in the flight environment
  • A wide variety of discharger designs is available on the commercial market. The inclusion of well-designed dischargers may be expected to improve airframe noise in P−static conditions by as much as 50 dB. Essentially, the discharger provides a path by which accumulated charge may leave the airframe quietly. This is generally accomplished by providing a group of tiny corona points to permit onset of corona-current flow at a low aircraft potential. Additionally, aerodynamic design of dischargers to permit corona to occur at the lowest possible atmospheric pressure also lowers the corona threshold. In addition to permitting a low-potential discharge, the discharger will minimize the radiation of radio frequency (RF) energy which accompanies the corona discharge, in order to minimize effects of RF components at communications and navigation frequencies on avionics performance. These effects are reduced through resistive attachment of the corona point(s) to the airframe, preserving direct current connection but attenuating the higher-frequency components of the discharge
  • Each manufacturer of static dischargers offers information concerning appropriate discharger location on specific airframes. Such locations emphasize the trailing outboard surfaces of wings and horizontal tail surfaces, plus the tip of the vertical stabilizer, where charge tends to accumulate on the airframe. Sufficient dischargers must be provided to allow for current-carrying capacity which will maintain airframe potential below the corona threshold of the trailing edges
  • In order to achieve full performance of avionic equipment, the static discharge system will require periodic maintenance. A pilot knowledgeable of P-static causes and effects is an important element in assuring optimum performance by early recognition of these types of problems
Volcanic Ash Advisory Centers
Figure 2: Volcanic Ash Advisory Centers

Case Studies:

  • NTSB Identification: , The National Transportation Safety Board determines the probable cause(s) of this accident to be: Inadvertent encounter with volcanic ash cloud, which resulted in damage from foreign material (foreign object) and subsequent compressor stalling of all engines. A factor related to the accident was: The lack of available information about the ash cloud to all personnel involved

Volcanic Ash Advisory Centers:


Conclusion:

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