NTSB Safety Alert SA-011 - Thunderstorm Encounters

Thunderstorm Encounters

IFR pilots need to actively maintain awareness of

severe weather along their route of flight

The problem

• NTSB in vestigations have identified accidents that a ppear to be wholly or partly

attributable to in -flight encounters with severe w eather.

• These accidents have all in volved aircraft ope rating under instrument flight rules and in

contact with air traffic controllers.

• Investigati ons sh ow that pilots were either not advised about areas of se vere w eather a head

or were given incomplete info rmation.

• Each pilot had r eadily available alternatives th at, if utiliz ed, wo uld have likely prevented the

accident.

• ATC traini ng and briefings to c ontrollers have not b een sufficient to ensure that pilots receive

the w eather advisories needed to support good in -flight w eather a voidance decisions.

• Examples:

A Mitsubishi MU-2 en route to

Panama City, Florida, entered radar -

depicted intense to extreme cell. No

ATC radar weather information

issued or requested. One fatality.

Argyle, Flori da 9-1-2006

A Cessna 210 en route to Manassas,

Virginia, encountered intense to

extreme level convective weather.

The pilot requested a deviation after

entering the area, but lost contr ol of

the aircra ft and crashed. No ATC

weather information provided. One

fatality.

Ludville, Ge orgia 4-19-2006

SA-011 October 2006 , revised December 2015

A Cessna 182 entered an area of

severe weather over the Gulf of

Mexico. Deviations discussed with

ATC, but no intensity information

provided by ATC or requested by the

pilot. One fatality, aircraft not

recovered.

Naples, Fl orida 6-20-2005

A Mooney M20J encountered an

intense to extreme thunderstorm and

broke up in flight. No ATC radar

weather information provided or

requested. Two fataliti es.

Newellton, L ouisiana 7-26-2006

How can pilots avoid becoming involved in a similar accident?

• Severe w eather a voidance is primarily your responsibility.

• The prima ry job of ATC is to ke ep IFR air craft sep arated. When t heir workload permits,

contr ollers are also required to provide ad ditional services such as weather advisories, and,

upon pilot request, su ggested headings to a void radar-displayed precipitation.

• The pr oper use of ATC weather advisory ser vices may be critical to your safety when

operating near a reas of convective acti vity.

• Approa ch control radar systems p rovide near -real-time weather d epiction. En route centers

receive we ather ra dar informa tion from Nati onal Wea ther Service N EXRAD sites that refresh

the color p recipitation data on A TC dis plays every 4 to 5 minutes. Be aw are that en route

weather displays may be a few minutes b ehind the storm and all ow extra dist ance from

reported intense precipitation, es pecially in front of fast -moving convective acti vity. Also be

aware that cockpit NEXRAD data can be 15 to 20 minutes older than indicated on the cockpit

display.

• ATC radar systems depict only precipitation. Cont rollers cannot use radar to wa rn of

turbulence, ici ng, free zing rain, or other ha zards to flight. H owever, the pre sence of

subst antial precipitation implies the existence of thun derstorm h azards such as severe

turbulence and hail.

• ATC w eather ad visories sho uld include the lo cation, e xtent, and int ensity of ra dar-observed

precipitation. The de scripti ve wo rds for int ensity we re recently changed to ensure

consisten cy across all ATC faciliti es. The old l evel 1 is n ow “light”; le vel 2 is “moderate”;

levels 3 and 4 are d escribed as “ heavy”; and l evels 5 and 6 are described as “extreme.” If

precipitation is de scribed to you without any referen ce to inten sity, a sk for the in forma tion so

you c an make a g ood decision about how to proceed.

SA-011 October 2006 , revised December 2015 • Not all ATC radar s ystems can provide int ensity information. In such situations, you should

be told “int ensity u nknown.”

• Some accidents a ppear to ha ve involved controller u ncertainty about whe ther the pilot was

visually a voiding se vere weather areas or needed radar weath er assistance. T he contr oller

thought the pilot was able to see what was ahead, a nd the pilot tho ught the contr oller was

watching out for him. It is especially impor tant that you advise contr ollers if yo ur flight

conditions change from visual to i nstrument, and that w hen operating in instr ument

conditions you regularly request u pdated information on radar-depicted weat her ah ead of

your aircraft.

• Be es pecially dili gent about as king for upda tes after being transfer red from o ne ATC facility

to anot her. The n ew controller may have better equip ment or be u sing a differ ent radar site

and have an enti rely different pic ture of w hat lies a head.

• Ambig uous use of the term “wh en able” h as also l ed to c onfusion. Some cont rollers use

“Clea red direct x xx when able” to mean “when weather permits you to turn saf ely on course,”

while pilots may u nderstand su ch an instr uction to me an “Go dir ect to xxx as soon as you

can navigate there.” In some c ases, this am biguity has apparently l ed pilots re ceiving A TC

weather a voidance assistan ce to conclu de that it was safe to turn di rect to the specified fi x,

resulting in subsequent entry into thunderstorms. If you ha ve any uncert ainty about whet her

a cour se change will keep you clear of con vective weat her, ASK!

• Give pilot r eports. C ontrollers use them to c onfirm th eir radar weather depiction, and to

obtain de tails such as cloud tops or the e xistence of icing that may not be available thro ugh

any ot her source. Pilot reports also help c ontrollers advise other aircraft about what to

expect and what to a void.

• The safest plan when avoiding s evere weat her acti vity is to entir ely avoid the a ffected a rea or

land and wait for it to pass. H owever, if you find y ourself in ne ed of ATC as sistance, a sk

specific questions. W here is it in relation to my route? What d oes it cover? H ow far away is

it? What in tensities do you s ee? What l ooks like the best way a round it?

• Make decisions about weather deviations as far in advance as p ossible. C ontrollers will

have more time to r espond to y our needs, per form a ny necessary coordination, and provide

you with the information you re quire to cond uct a safe fligh t.

• Pay attenti on to wea ther alerts broadcast by A TC, esp ecially SIGMETS and Center Weather

Advisories, and obtain further details from HI WAS or Flight Watch if the ad visory is anywhe re

along or near your route. Flight Watch can also supply “big pictu re” weath er info rmation

beyond what ATC may have time to pro vide to you.

• Beco me familiar with the various on -board weath er avoidan ce tec hnologies a vailable,

including data-linked onboard NE XRAD weather ser vices, and c onsider whether the

additional information will help you to avoid encounters with severe weath er.