MEATBALL June 2006

WEATHER WISE

Lt Kunal Dey

Penetrating Thunderstorms

Having conquered so many feats in the world of aviation and with technology that improves with every passing second, Man has considerably reduced the numbers of accidents that occur in the air. Today’s airspace is the busiest ever, but again, flight safety has improved manifold ensuring safe conduct of flight even in this big rush. Flying today is much safer than probably what it was a decade ago.

Despite all this, it is important on our part to stick to the laid down procedures and strive for a safe flight, as there exist a number of factors that can cause disaster. One such enemy of aviation and undoubtedly the most dangerous is a thunderstorm. A thunderstorm is an “either/or” situation, i.e. either you’re in it or you aren’t. Avoiding it by as large margins as practicable and that too well in time is the key to a safe flight.

All thunderstorms are potentially dangerous and their external appearance is no guide to the severity of hazards that may be expected. Aviation hazards associated with thunderstorms (not in any order of priority) may be stated as:

Ø      Base Height. Once dissipation occurs and thunder and precipitation starts, the cloud base become so low that terrain clearance beneath the clouds becomes difficult to maintain.

Ø      Poor Visibility. At times, inside the thunderstorm, visibility may drop to as low as 20 meters.

Ø      Hail. Damage from hailstones can be considerable, especially to radomes and transparencies. Hail can be met anywhere in or under the storm, even an overhanging anvil.

Ø      Icing. Thunderstorm clouds give icing problems both in engine and airframe. Serious loss of power may be experienced in piston engines, whereas a turbine engine may even suffer a flame out. Airframe icing result in increased weight, disturbed relative airflow decreasing lift and increasing drag. Even the control surface may become ineffective.

Ø      Instrument error. Turbulent airflow around the aircraft and the localised variations in pressure can cause rapid and serious errors in the reading of altimeters, VSI and ASI. The assurance of the magnetic compass may also get seriously affected due to the realignment of magnetic lines of force in case of a lightning strike.

Ø      Lightning. In a thunderstorm, lightning may occur at any level, but is most likely in regions of temperatures between +6 to –10 deg c, i.e. in a 10.000ft band about the freezing level. It may cause distraction to the crew and may even lead to temporary blindness of the pilot. The high probability of a total electrical failure worsens the situation.

Ø      Squalls, Windshear and Microburst. Thunderstorms with a low cloud base near the airfield have been known for their notoriety in causing accidents on approach and take off.

Ø      Precipitation.  Precipitation from a thunderstorm reduces forward visibility considerably and near an airfield may pose serious problems to arriving or departing aircraft due to wet runways, downdrafts and poor visibility.

Ø      Static. Static may seriously jeopardise the efficient functioning of communication and radio navigation equipment on board.

Ø      Turbulence. It makes the aircraft difficult to handle and indeed, incorrect handling can lead to loss of control. If the aircraft is flown at a speed higher than its thunderstorm penetration speed as specified in the flight manual, it stands a risk of structural failure. On the other hand, lower than recommended speed may lead to the aircraft stalling. Turbulence may also lead to airsickness of the crew and prolonged exposure may have serious consequences.

Now that we know the flight safety hazards of a thunderstorm, let us now take a look at preventive measures and remedial actions that aviators needs to take in order to minimise its effects and ensure flight safety:

Ø      Whether due to unavoidable circumstances or if in the vicinity of Cumulonimbus clouds, a pilot must endeavour to fly at this speed, so as to minimise damage to the airframe and at the same time, maintain sufficient effectiveness of all control surfaces.

Ø      Switch on pilot heaters and all anti-ice and de-ice equipment to prevent icing.

Ø      In case of a turbine engine, select continuous ignition to prevent the engine from flaming out.

Ø      Do not rely on pressure instruments, as the reading may be dangerously erroneous. Even the magnetic compass should not be depended upon as magnetic anomalies can affect the reading. The key here is to rely on the artificial horizon and other gyroscopic instruments.

Ø      To avoid the distraction and blinding effects of lightning, wind up the cockpit lightning to full. It would be a good idea for at least one of the operating pilots to wear dark glasses as an insurance policy, should the other pilot be blinded. In fact lightning can be used—especially at night—to supplement the aircraft’s weather radar for pinpointing and subsequently avoiding the most active storm areas.

Ø      If on the approach in thunderstorm conditions it is found that abnormal levels of power are necessary to maintain the airspeed, attitude and glide slope, then a wind shear go-around should be initiated well in time.

To be safe in the air, a pilot must learn to respect weather; the sooner he does it, the better it is, not only for him but also for the organisation he serves. He must always remember that mission accomplishment is important, but flight safety is paramount. He always insist on a detailed met briefing before getting airborne, and once airborne, must always strive to keep a sharp and constant vigil on weather using all the resources available to him. As it has been said many o times:

 “A SUPERIOR PILOT IS THE ONE WHO USES HIS SUPERIOR JUDGEMENT TO AVOID SITUATIONS WHICH REQUIRE THE USE OF HIS SUPERIOR SKILLS”