시동을 걸기 직전 창문을 열고 큰 소리로 외친다. 비행기 주변에 있는 사람들에게 엔진 작동을 알리는 말이다. 멈춰있던 비행기가 진동하며 움직이기 시작한다. 관제사의 이륙 허가를 받고 천천히 스로틀을 밀어 파워를 올리면 활주로를 달리던 비행기는 하늘로 날아오른다. 조종사의 능숙한 조작과 자연의 바람이 만나 1톤에 달하는 육중한 기계는 살아 움직이는 생물이 된다.
밤마다 같은 꿈을 꿨다. 새처럼 하늘을 날며 내가 살던 동네 곳곳을 내려다보는 꿈이었다. 어린 마음에 그 능력 하나면 세상 전부를 다 가진 기분이었다. 잠에서 깨면 눈을 감고 그대로 누운 채 꿈의 잔상을 떠올리며 행복에 젖어들었다.
꿈을 직접 느끼고 싶었다. 미국으로 떠났다. 1년 동안 비행학교에서 공부하고 훈련하면서 미국과 한국의 사업용 조종사 면허를 취득했다. 내게 남은 건 단순한 손바닥만 한 자격증이 아니다. 길을 걷다가도 눈 감고 뺨을 스치는 바람을 느끼다 보면 그때 그곳으로 돌아가 비행하는 나를 만난다.
There are 5 in-flight weather advisories that are forecast based on actual weather conditions.
1. Convective sigmet [WST]
advises of weather that is convective in nature and is issued for every thunderstorms with hail greater than 3/4“, surface winds greater than 50 knots
tornadoes, embedded thunderstorms, lines of thunderstorms
thunderstorm producing precipitation
Convective sigmet also implies severe turbulence, icing, and low-level wind shear
valid for 2 hours
2. Sigmet [WS]
advises of non-convective weather that is potentially hazardous to all aircrafts
issued for severe turbulence and icing not associated with convective activity, dust storms and sand storms reducing visibility below 3SM, and volcanic ash
valid for 4 hours
3. Airmet [WA]
advises of weather that is lower in intensity
valid for 6 hours
there are 3 types of Airmet
Sierra – IFR or mountain obscurations.
Tango – moderate turbulence, sustained surface wind of 30 knots or greater, and non-convective low-level wind shear.
Zulu – moderate icing.
4. CWA(Center Weather Advisories)
is issued on an unscheduled basis as supplementary information to an existing WA, WS, or WST
usually occurs when the temperature of air near the ground is cooled to the air’s dew point
Types of fogs
Radiation fog, image from PHAK 12-21
Radiation fog : On clear nights, with little to no wind, radiation fog develops. It usually forms in mountain valley. It occurs when the ground cools rapidly due to terrestrial radiation, and the surrounding air temperature reaches its dew point.
Advection fog : When a layer of warm, moist air moves over a cold surface, advection fog occurs. Wind(up to 15knot) is required to form advection fog. It is common in coastal areas where sea breezes can blow the air over cooler landmasses.
Upslope fog : When moist, stable air is forced up sloping land features like a mountain range, upslope fog occurs. Wind is required to form it.
Steam fog : When cold, dry air moves over warm water, steam fog occurs. Steam fog is common over bodies of water during the coldest times of the years.
Ice fog : When the temperature s much below freezing and water vapor forms directly into ice crystals in cold weather, Ice fog occurs.
a local storm, always produced by a cumulonimbus cloud, and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail.
How to develop
Unstable air, high moisture, and uplifting force are all required for thunderstorm to form
3 stages of thunderstorm
Life cycle of thunderstorms, image from PHAK 12-28
Cumulus is marked by a large billowing clouds with extensive vertical development, which is caused by updrafts from surface heating, terrain, pressure system or fronts
Mature is marked by the beginning of rain at the surface. During this stage, updrafts are at their maximum and extreme vertical shearing occurs between the updrafts and the cooler downdrafts following the precipitation
Dissipating is marked by downdrafts. The cool downdrafts eventually terminate the uplifting forces. When the downdrafts end and the rain has stopped, this signifies the end of the dissipating stage
If a radar indicates thunderstorm activity, pilots should avoid the cells by at least 20 miles.
Two different categories
Airmass TS is generally caused by surface heating (at desert or sea)
Steady state TS is associated with weather systems and frontal movement
Three principal types
Single cell (=ordinary cell thunderstorms) consists of only one cell. It easily circumnavigated by pilots except at night or when embedded in other clouds. Single cell thunderstorms are rare. Almost all thunderstorms are multi-celled.
Multicell cluster and line consists of a cluster of cells at different stages of their life cycles. As the first cell matures, it is carried downwind, and a new cell forms upwind to take its place. A multicell may have a lifetime of several hours (or more), which makes it tougher to circumnavigate than a single-cell thunderstorm. May have supercells embedded within them.
Supercell consists primarily of a single, quasi-steady rotating updraft that persists for an extended period of time. Updraft speeds may reach 9,000 fpm (100 knots). They may persist for many hours (or longer) and their size and persistence make them tough to circumnavigate.
Any occurrence in the airport runway environment involving an aircraft, vehicles, persons, and objects that can create a collision hazard or results in a loss of required separation with an aircraft taking off, intending to take off, landing, or intending to land.
It requires someone to be at fault
Pilots, controllers, and vehicle operators can cause runway incursions
How to prevent
Familiarity with the airport layout by studying an airport diagram
Visually clearing the length of the runway and the approach area before taxing across or onto the runway
Reading back all runway instructions in full
Turning on all exterior lights before crossing the runway holding short marking
Situational awareness at all times while on the airport surface
June-Young Lee 