Navigating Around Adverse Weather Conditions

By; Captain Faik Sava? üSKENT

? December 19, 2024

How to navigate around WX systems using available means:

In airline business or any other commercial air transportation busines, be it a scheduled or an unscheduled flight, the first thing typically a pilot does; is to go to the relevant Dispatch Office or Flight Information Center (FIC. The aim is to receive a Standard Briefing about the intended flight route, present and forecast weather conditions, prevailing NOTAMs (Notice to Air Missions), and to get the airline’s stored flight plan or to file a new one when necessary.

Most of the dispatch offices and FICs have real time weather information and observations, altitude winds (winds aloft) and temperatures, significant meteorological (SIGMET) information to be presented to the pilots in a “Flight Folder” along with the valid enroute NOTAMs. They also generally have proper equipment to present satellite or radar view of the related terminal area, enroute, enroute emergency alternate, destination and destination alternate airports. It all depends the capability of the relevant dispatch office and dispatch officers.

Additionally, an onboard ACARS system (Aircraft Communication Addressing and Reporting System) with printer, is usually ready and handy for the pilot usage in most of the airliner flight decks to receive updated information should need arise.

High altitude wind information entered into aircraft FMS systems can be updated quickly at any time during the flight.

Thanks to today’s technology, Radar and Satellite weather view of a geographical area of interest is possible even via an internet connection. However, weather phenomena can rapidly change within minutes. Therefore the importance of real-time information cannot be underestimated.

USA has also an established NEXRAD system although there would be a delay between a cockpit view and actual weather situation in the area. The Next Generation Weather Radar (NEXRAD) system is a network of 160 high-resolution S-band Doppler weather radars jointly operated by the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the U.S. Air Force.

New generation aircraft airborne weather radars have excellent capabilities to detect weather activities that might be hazardous to air operations.

When operating in the automatic mode, multiple radar scans at pre-selected tilt angles detect; short, mid, and long range weather pictures at the selected range. In auto mode, tilt and gain inputs are not required. This results in a satisfactory weather detection at the selected ranges in all phases of flight. Caution is required to remain in automatic mode, since when unintentionally exiting out of the auto mode, some radar types fall into minimum gain mode, that might create the root cause of flying into an embedded storm incident.

An important thing to remember in airborne weather radar philosophy is that; “turbulent area can be sensed by the weather radar only when there is sufficient precipitation”. Therefore; CAT (Clear Air Turbulence) cannot be sensed by an aircraft radar. In this respect; the weather radar also provides predictive windshear warning or alerting.

System processing ensures data from thunderstorm tops within 5,000 feet, remain on the cockpit radar display until it no longer poses a danger. This, enables flight around thunderstorms that may not be visually detected.

Deviation around a storm during the cruise phase is called a circumnavigation. This is preferably done on the windward side of the storm cell to avoid any rapid movement of the TS cell downwind. A pilot should never attempt to fly under the anvil of a CB (cumulonimbus) cloud.

?While flying in today’s EFIS (Electronic Flight Instrument System) and FMS (Flight Management System) equipped airplanes, reading the actual wind at the altitude is so easy that only a blind can’t see it.

Almost all Navigation Displays (ND) show digitally “wind direction and speed” along with a “wind arrow” that is typically in White color. Therefore, indications of wind bearing, speed, and direction, with respect to display orientation and heading/track reference is available for pilots at all times during flight. The ND indicators also function as the airborne weather radar display in selected modes.

Lightning activities can extend to several miles out of a TS cell; therefore, a safe distance should be maintained between a TS cell and an aircraft. ?

Lightnings are not very hazardous to airliners any more, but this shouldn’t change precautionary operating procedures.

The technological improvements in Nitrogen Generation System (NGS), that converts bleed air to nitrogen-enriched air to reduce flammability of center wing tank fuel vapors during all phases of flight, developing flame arresters, reduced flammability of the present jet fuels and improved innovative design of the airliners helped reduce the lightning hazards to airliners.

Cold front crossing is generally easier than a warm front crossing. Because warm front TS cells are generally hidden and only visible via radar. In other words; they are imbedded.

Previous airborne WX radars used to have more problems for detecting hazardous huge TS cells due to “attenuation or shadowing” problems than today’s radars.

Radar attenuation is the "absorption of radar transmission signals" when radar pulses enter an area of very heavy density or extreme precipitation. This can prevent airborne weather radar from accurately detecting any cell activity.

A signal that is fully attenuated means; a signal that is fully absorbed. Should no pulses return to an a/c’s radar receiver, the appearance would be “blank, in other words; “dark” on the display. Therefore; shadowing causes the shape and intensity of the weather displayed to the pilot not to be accurate.The more intense the precipitation, the less distance the radar can see into a storm cell. What appears to be a thin crescent-shaped band of precipitation could be only a small part of a much larger area of extremely heavy precipitation.

Attenuation can also occur when heavy rain or ice builds up on a radome, this becomes even worse when an a/c radome paint is improper, radome is damaged or not well maintained. This situation may endanger flight safety by creating a significant obstacle to accurate detection of dangerous CB activities that can change its shape rapidly and violently.

As a tip for avoiding shadows: “Tilt your radar down far enough to paint the ground and look for the ground returns behind this blank area”.

The use of an airborne weather radar requires expertise, vigilance and knowledge to identify multi-cell storms, a squall line, a supercell and etc. When using an aircraft radar in auto gain in some airborne weather radar types; an unintentional light touch might take the radar into minimum gain status. That might be dangerous during warm front crossings.

Therefore every and each airline pilot should undergo a special airborne weather radar usage course given by professional specialists. I personally had received a course given by one of the most precious pilots of his times, Archie Trammell. He died in 2018 may he RIP.

Recent airborne weather radar systems have improved systems to minimize radar shadowing / attenuation problems.

Also the reflectivity of the precipitation particles varies depending on the type of the particles in the cell. Rain, wet hail and wet snow are much more reflective than dry particles such as dry hail, ice crystals and dry snow. I can even say that, an aircraft radar can hardly see any frozen precipitation.

Should an airliner flying its planned route and profile (cruise speed and altitude) encounter strong headwinds and/or Clear Air Turbulence (CAT), normally pilots would like to change either their altitude or heading or reroute for their destination.

Changing altitude would be easier but detouring or rerouting would be costly in respect of time, money and sustainability.

For the advantages and disadvantages of an altitude change , normally a pilot should refer to FCOM’s “performance inflight “ section CRUISE WIND-ALTITUDE TRADE table. This can be reached via onboard EFBs (Electronic Flight Bag) as well.

After referring to the appropriate tables the PIC decides whether to change the cruise level or to reroute.

During Weather Front crossings, cold front squall line TS cells are mostly visible by naked eyes during daylight. On the contrary, a warm front mostly have imbedded TS cells that won’t be visible by naked eyes. ?In both cases; as approaching to a weather front to cross, at least 60-80 miles away (roughly 8-10 minutes earlier) with the proper usage of the airborne wx radar, the decision about “where to” and “how to“ or “not to” cross the front or squall line should be given.

How to includes;

1. Proper usage of the airplane radar with expertise.

2. Setting the turbulent weather penetration speed (even if there is no turbulence at that moment).

3. Switching the passenger seatbelts signs to on, making a PA and informing the cabin crew.

4. For jet engines; selecting the Continuous Ignition (if required by the airplane type),

5. Reviewing the proper usage of the autopilot modes in turbulent weather.

6. Using Thermal Engine Anti-ice system (as required by the AFM).

7. As closing to the cells trying to keep minimum 5 to 10 NM distance away from each cell while either circumnavigating or crossing between them.

8. Pilots need at least 10-20 NM gap between two TS cells to cross.

9. Before crossing be sure the back side of the cells are clear of activity via once in a while adjusting airborne radar tilt down to paint the terrain on radar display. This will guarantee that there is no shadowing.

The summary of general Rules near thunderstorm activities:

1. Avoid all thunderstorms. It’s always the best policy. Never attempt to fly over a TS that has a top at or above 35000 feet. Do regard any thunderstorm with tops 35,000 feet or higher as extremely hazardous whether the top is visually sighted or determined by your airborne weather radar.
2. Never come closer than 5 NM to any CB cloud with overhanging areas, and consider increasing that distance to minimum 20 miles in cases of severe CB activity if possible. You can encounter hail and violent turbulence anywhere within 10-20 miles of severe thunderstorms.
3. Remembering the destructive potential of shear turbulence; do not attempt flight beneath thunderstorms,
4. Use recommended turbulent air penetration speed.
5. Maintain your sound judgment.
6. Jet aircraft can safely fly over thunderstorms only if their flight altitude is well above the turbulent cloud tops. IMHO minimum 5000 feet separation is required. Never overfly a TS cloud which has a top at 35000 or above. The most intense storms are often the tallest storms, seek to go around them.
7. As the arriving aircraft approach their destination airport which is under the impact of heavy CB activities, the pilot will usually be asked to slow down or enter a holding pattern until the thunderstorms in and around the airport have cleared. As more planes arrive and holding continues, over-crowded airspace and running down the fuel to minimum diversion fuel or to minimum fuel can become problematic. If thunderstorms persist, holding aircraft will divert to alternate airports, wait out the bad weather, refuel, and fly again later to the original destination. Diversions are undesirable because of the magnitude of passenger delay and cost to airlines.
8. Don’t land even if you can see through to the other side or takeoff in the face of an approaching thunderstorm. Low-level turbulence, wind shear, microbursts under or in the vicinity of the storm could be hazardous and could cause loss of control inflight (LOC-I).
9. Don’t attempt to fly under the anvil of a thunderstorm. There is a potential for severe and extreme CAT (clear air turbulence).
10. Don’t fly without airborne radar into a cloud mass that might contain scattered embedded thunderstorms. Don’t trust the visual appearance to be a reliable indicator of the level of turbulence inside a TS.
11. Don’t assume that ATC is capable and thus will offer radar navigation guidance around thunderstorms.
12. Don’t use NEXRAD mosaic imagery as the sole means for negotiating a path through a thunderstorm area for tactical maneuvering. Do remember that the data-linked NEXRAD mosaic imagery shows where the weather was, not where the weather is (The weather picture may be 15 to 20 minutes older).
13. Do listen to chatters on the ATC frequency for Pilot Reports (PIREPs).
14. Do ask ATC for radar navigation guidance when it’s properly equipped, or to approve deviations around thunderstorms.
15. Do use NEXRAD imagery, Flight Information Service-Broadcasts to avoid stormy areas entirely via strategic maneuvering. In this case the contingency fuel reserves might turn out to be insufficient. Recalculation of your fuel needs will be required.
16. Conforming to position reporting procedures, do clearly advise the relevant ATCs while switching to another controller, especially when their traffic monitoring capabilities are not matched, that you are deviating for thunderstorms yet to rejoin the original route.
17. Do avoid by at least 20 miles any thunderstorm “identified as severe”.
18. Do circumnavigate the entire area by strategic maneuvering if the area has more than 6/10 thunderstorm coverage.
19. Although not always, do remember that vivid and frequent lightnings might sometimes indicate the probability of a severe thunderstorm.
20. Do give an instant PIREP with proper phraseology for the adverse weather conditions when encountered.

Although it’s hardly possible by the application of proper measures, if you’re still unable to avoid penetrating a thunderstorm;

• If the aircraft inadvertently penetrates the thunderstorm, maintain a straight and level attitude on a heading that will take you through the storm area in the minimum time. Additionally, turning maneuvers increase stress on the aircraft while decreasing the lift.
• Turn the Altitude Hold switch to off if autopilot is engaged.

• Ensure your safety belt is tightened and your shoulder harness is on, and loose gear secured. All of these precautions should have been done already while in the vicinity of the stormy area.
• Maintain the heading to take the aircraft through the storm in minimum time.
• Verify that pitot heat is on and turn on the thermal engine anti-ice. Severe icing can be rapid.
• Establish power settings for turbulence penetration airspeed recommended in the AFM. Don’t change power settings; disengage auto throttle/ auto thrust and maintain settings for the recommended turbulence penetration airspeed.
• During night, turn up cockpit lights to high intensity to lessen temporary blindness from lightning or use storm lights when available.
• If using autopilot, disengage Altitude Hold Mode and Speed Hold Mode. The automatic altitude and speed controls will increase maneuvers of the aircraft thus increasing structural stress.
• If using airborne weather radar, tilt the antenna up and down occasionally. This will permit the detection of other thunderstorm activity at altitudes other than the one being flown.
• Keep your eyes on the flight instruments.
• Allow the altitude and airspeed to fluctuate.
• Remember that a thunderstorm cell’s life-cycle changes from 30 minutes (non-severe) to hours (severe) and if not stationary, they travel at speeds up to 60 knots.

By Captain Faik Sava? üSKENT ? December 19,2024