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An Encounter With A Microburst

It was a beautiful pre-summer afternoon as we took off from Bangalore for Coimbatore in our Dornier-228. We were required to position at Coimbatore for a routine charter flight. The weather forecast for the route was seasonal pre-monsoon weather with likely Cumulonimbus buildup during late afternoon. The enroute weather was generally good, except for a large cell visible on the weather radar slightly north of Coimbatore. Our track was fortunately clear and we expected no problems but for the northerly winds, which were pushing the cell slowly towards our destination. However, we expected to be on ground well before the CB could affect our destination. As we approached Coimbatore, the tower cleared a scheduled Boeing-737 flight to descend behind us and join the ILS final approach path directly ad told us to report overhead for a procedure ILS, as requested by us. However, as we reported overhead, the mighty CB had reached within 10 NM of the airfield and moving in fast. Winds were slowly picking up and we were anxious to be on ground as early as possible. In the meanwhile, the B-737 reported as having been established on ILS for R/W 23. As we joined the hold for the ILS, the jet reported some turbulence on finals. However, as the jet landed, the captain informed us that he had experienced severe turbulence on finals and advised us to approach the airfield from the other end, I e R/W 05.

Sensing an abnormal situation developing, we became adequately alert and decided to follow his advice. The CB was now within 5 NM from the airfield.

As we decided to join a southerly visual circuit, the winds too were veering and becoming favorable for our newly selected approach path. Consequently, we joined a descending circuit and were asked to report finals for R/W 05. By the time we turned base-leg, we had reached circuit altitude and began adjusting configuration for the final approach. We also noticed slight turbulence at this stage.

Further, one important variation was the requirement of higher power setting for the existing aircraft configuration and altitude. As we turned finals, the power setting requirement steadily increased. During descent, the power requirement increased uncomfortably and reached an abnormally high setting of 65% torque by the time we were 500 feet on short finals. The normal setting under the circumstances would have been 35% torque on finals and steadily decreasing during the final descent. In addition, there was a steady increase in turbulence level and situation had become uncomfortable at 500 feet. We were now in a full-fledged Microburst and slowly getting into a worse situation. The captain, on RHS who was silently monitoring the approach finally decided to takeover the controls and commenced a go around at about 400-500 feet. As he opened power, he found that the aircraft was barely maintaining height with even maximum power and turbulence was now severe, lightning at night

especially for a light aircraft like Dornier. At this crucial stage, the Captain decided to leave current flight path and commenced a right turn away from the direction of winds and the approaching CB, which by now was very close to the far end of the runway. To his great relief the effect of strong winds of microburst began to fade away, the aircraft started to respond to power, and finally started a gradual climb at about 200 feet above ground level. With further change in direction, the aircraft comfortably climbed out and we decided to divert to the nearby airfield.

Aware that we had had a real close shave, the following points emerged during the mutual debrief:

The caution from the Boeing was indeed a timely one regarding the oncoming situation.
We had inadvertently entered a microburst and recovered just short of a sure disaster.
There is no known equipment to accurately warn the pilots about an impending microburst, which can be present in clear weather in the vicinity of a CB.
Within a microburst, the turbulence can drastically increase from an acceptable level to a dangerous one within a short descent of 200-300 feet.

The wind situation for us while in microburst changed sequentially from strong headwinds to strong updraft and then to a severe downdraft, the last condition being responsible for many aviation disasters where even maximum power from all the engines may be insufficient to climb out safely. Fortunately, we avoided getting into this last situation, as we decided to turn without waiting for the aircraft to initiate climb at fairly low altitude. Incidentally, the Captain vaguely remembers this action being recommended on a TV program on aviation disasters as a likely course of action for an airliner, which crashed due to a microburst some years ago. You never know which direction the help can eventually come from!

The decision to divert could have been taken right away. Although we did not expect to encounter a microburst, yet avoiding this situation altogether would have been a desirable course of action. However, we would have been deprived of this once in a lifetime experience of encountering a microburst first-hand, and coming out alive and safe. The encounter will never fade away from our memory. And of course, I have absolutely no desire to get into a similar situation in future.

Most important message from this incident was reinforcement of the famous flight safety adage “it can happen to you”.

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