Monday, May 29, 2017

Delta Air Lines, Airbus A320-211, N332NW: Incident occurred August 07, 2015 in Max, Dundy County, Nebraska



The National Transportation Safety Board traveled to the scene of this incident.

Additional Participating Entities:

Federal Aviation Administration;  Washington, District of Columbia
National Air Traffic Controllers Association; Olathe, Kansas
Delta Airlines, Inc.; Atlanta, Georgia
BEA - Accredited Representative; Le Bourget, France
ALPA, International; Herndon, Virginia
General Electric; Cincinnati, Ohio

Aviation Incident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf


Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms


Aviation Incident Data Summary - National Transportation Safety Board: https://app.ntsb.gov/pdf


Delta Air Lines Inc: http://registry.faa.gov/N332NW 

NTSB Identification: OPS15IA020

Incident occurred Friday, August 07, 2015 in Max, NE
Probable Cause Approval Date: 03/29/2017
Aircraft: AIRBUS INDUSTRIE A320 211, registration:
Injuries: 124 Uninjured.

NTSB investigators used data provided by various sources and may have traveled in support of this investigation to prepare this aircraft incident report.

The captain and first officer were operating Delta Air Lines flight 1889 as a regularly scheduled passenger flight that was originally scheduled to depart General Edward Lawrence Logan International Airport, Boston, Massachusetts, at 2130 coordinated universal time (all times in this report are in coordinated universal time unless otherwise noted), but air traffic control (ATC) delayed the departure until 2225. According to a review of automatic communication and recording system data, the flight release was generated and transmitted to the flight crew at 2103. According to the company flight dispatcher located at the Delta Operations Control Center, it included an ATC-preferred routing to Salt Lake City International Airport, Salt Lake City, Utah, because "there wasn't much weather enroute prior to getting out to the west." The dispatcher sent the initial weather briefing for the flight to the flight crew at 2106. At 2150, the dispatcher sent an updated weather briefing, which indicated that there were no weather updates since the previous transmission. The flight departed at 2244. 

The National Weather Service (NWS) Storm Prediction Center day 1 convective outlook and area forecast that were issued and valid before the incident flight crew received their preflight weather information forecast areas of severe weather along the flight route and areas of thunderstorms, possibly severe, respectively, along the flight route. Although the preflight weather package discussed a chance of afternoon thunderstorms around the destination airport, it did not mention thunderstorm activity along the flight route.

A review of meteorological information indicated that the NWS also issued a severe thunderstorm watch for the incident site and surrounding area at 2105 with severe weather possible through 0500, which was along the originally planned flight route. Further, the NWS issued a severe thunderstorm warning for the area north of the airplane's flightpath as early as 0133, at which time the incident flight was about 230 miles east-northeast of the incident location. This information would have been available to the company dispatcher; however, the dispatcher did not pass either the severe thunderstorm watch or warning information to the flight crew before or during the flight. 

At 0129, the Minneapolis Air Route Traffic Control Center (ZMP ARTCC) controller, who was handling the flight at that time, initially advised the flight crew about a large area of moderate-to-extreme precipitation on their current flight route in western Nebraska and that they would likely need to significantly deviate to get around it. The company dispatcher reported that he also observed the weather. At 0138, he sent a message to the flight crew indicating that there were thunderstorms ahead of the flight that extended up to 60,000 ft; suggesting that they fly direct to Thurman, Myton, and then continue on their planned flight route; this amended routing would take them further south of their original routing toward a gap in the developing thunderstorm activity. The dispatcher also indicated that he had sent the flight crew turbulence plot (TP) CN11, which was issued at 0049. Delta Air Lines had issued TPs for thunderstorm activity at 0113 (TP CN12) and at 0159 (TP CN13), both of which indicated potential thunderstorm activity along their flight route. However, the dispatcher only transmitted TP CN11, which did not include information about thunderstorm activity along the flight route. According to the captain, the revised routing put them directly toward a gap in the weather that corresponded with what they observed on their weather radar.

At 0141, the ZMP controller again informed the flight crew of the large area of moderate-to-extreme precipitation at their 12-o'clock position and 130 miles out and advised them of the decisions of other flight crews of flights headed in that direction to deviate well north or south around the area of precipitation. Two minutes later, the flight was transferred to the Denver (ZDV) ARTCC; at that time, the weather radar data available to both the ZDV controller and the company dispatcher indicated that the gap between the two areas of thunderstorms had reduced from 30 to 26 miles. The pilots queried ZDV about the line of thunderstorms ahead of them and were advised that there was a gap in the weather, which the pilots noted corresponded to the dispatcher's earlier suggested route. The flight crew chose to continue toward the gap in the weather, and both pilots believed they would be able to maintain at least 20 miles lateral separation between each individual thunderstorm cell, as required by Delta Air Lines procedures for thunderstorm avoidance. By 0154, with the flight still more than 50 miles from the thunderstorms, the gap in thunderstorm activity had closed to 12 miles. At the time that the flight entered the gap, the distance between the areas of thunderstorm activity had reduced to less than 10 miles and was continuing to decrease. 

Also about 0154, the pilot of eastbound Southwest Airlines flight 3318, which had just passed through the hole in the weather in the opposite direction, provided a pilot weather report (PIREP) to the ZDV controller indicating that the hole was starting to close and that he did not think anybody should go through it behind them. However, the ZDV controller did not provide this PIREP to the incident flight crew. Also about 0154, as the incident flight was about 50 to 60 miles from the thunderstorms, the pilot of eastbound American Airlines flight 1155, which had passed the incident flight earlier in the opposite direction, reported a dramatic temperature increase at cruise altitude. Despite the ZDV controller's awareness of the weather conditions from the PIREPs, he did not relay this information to the Delta flight, which continued toward the thunderstorms. 

According to the incident captain, he also noted a temperature increase at cruise altitude followed by a "rough ride" and "static discharge" and was briefly unable to hear the radio due to the static interference. The captain decided to turn away from the weather, and the ZDV controller provided him a heading to avoid the weather. As the airplane began to turn left, their radar display showed additional weather, and the flight crew chose to turn back to the right. The flight then began to encounter hail, which shattered the outside panes of the forward windows. The captain declared an emergency and diverted to Denver International Airport. 

The ZMP controller did an excellent job of relaying known weather information to the flight crew. However, the ZDV controller did not. Specifically, the ZDV controller failed to issue the displayed weather to the flight as required by Federal Aviation Administration (FAA) Order 7110.65, "Air Traffic Control." The ZDV controller also failed to disseminate significant PIREP information to the incident flight crew as required by FAA Order 7110.65. Further, the company dispatcher who provided the flight crew with the initial and revised preflight weather briefings did not provide adequate weather information to the flight crew because it did not include information about the thunderstorm activity forecast along the flight route, and the dispatcher subsequently failed to provide the flight crew with complete and timely weather information, including weather radar data information, while the flight was en route to the destination airport.

The National Transportation Safety Board determines the probable cause(s) of this incident as follows:
The flight crew's continued flight into a closing gap between areas of thunderstorm activity and their failure to maintain the required lateral separation from the thunderstorms, which resulted in the airplane's encounter with hail and subsequent airplane damage.

Contributing to the incident were the company flight dispatcher's failure to provide complete and timely weather information to the flight crew and the Denver air route traffic controller's failure to provide significant pilot weather report information and alert the pilots of existing and worsening hazardous weather along their flight route, as required by Federal Aviation directives, both of which led to the airplane's encounter with hail.




HISTORY OF FLIGHT

On August 8, 2015, about 0202 coordinated universal time (all times in this report are in coordinated universal time unless otherwise noted), Delta Air Lines flight 1889, an Airbus A320-211, N332NW, penetrated a thunderstorm and encountered large hail while in cruise flight at flight level (FL) 340 over Max, Nebraska. The flight crew declared an emergency and diverted to Denver International Airport (DEN), Denver, Colorado. None of the 119 passengers, 2 pilots, and 3 flight attendants sustained injuries, and the airplane sustained minor damage. The flight was being operating as a 14 Code of Federal Regulations (CFR) Part 121 regularly scheduled passenger flight from General Edward Lawrence Logan International Airport (BOS), Boston, Massachusetts, to Salt Lake City International Airport (SLC), Salt Lake City, Utah. Night instrument meteorological conditions were reported along the route of flight at the time of the incident.

The flight was originally scheduled to depart BOS at 2130, but air traffic control (ATC) delayed the departure until 2225. According to a review of automatic communication and recording system (ACARS) data, at 2103, the assigned flight dispatcher, located at the Delta Air Lines Operations Control Center (OCC) in Atlanta, Georgia, generated a flight release and sent it to the flight crew. According to the dispatcher, it included an ATC-preferred routing to SLC because "there wasn't much weather enroute prior to getting out to the west." At 2106, the dispatcher sent the flight crew an initial weather briefing for the flight, which noted that there was a chance of afternoon thunderstorms around the destination airport. At 2150, he sent an updated weather briefing indicating that there had been "no weather updates since the previous transmission."

The airplane taxied from the gate in BOS at 2229 and departed at 2244. The climb to FL340 and initial cruise were uneventful. The first officer was the pilot flying (PF), and the captain was the pilot monitoring. 

In post incident interviews, the captain reported that, as the flight progressed through Minneapolis Air Route Traffic Control Center (ZMP ARTCC) airspace, he and the first officer observed a line of thunderstorms ahead of the airplane on the weather radar. The captain added that he was operating the weather radar manually and using the "calibrated" mode to view the weather. 

At 0129, the ZMP controller initially advised the flight crew about a large area of moderate-to-extreme precipitation on their current flight route in western Nebraska and noted that they would likely need to significantly deviate to get around it. The company dispatcher reported that he had also observed the weather and, at 0138, he sent a message to the flight crew via ACARS indicating that there was a cluster of cells ahead with tops to FL600 and thunderstorms east of SLC, resulting in a lot of holding, and suggested that they amend their routing and proceed direct to Thurman (TXC), Myton (MTU), which would take the flight south of its original routing as it flew east to west around Denver. He also noted that he sent them turbulence plot (TP) CN11. The captain reported that the revised routing would have put them directly toward a gap in the weather that he observed on the weather radar.

A review of ATC transcript information from between 0129 and 0141 revealed that four other aircraft traveling westbound to various destinations in the western United States at similar altitudes were making significant deviations to the north and south around the weather developing in western Nebraska. At 0141, the ZMP controller again informed the flight crew of the large area of moderate-to-extreme precipitation at their 12-o'clock position and 130 miles out and advised them of the decisions of the other flight crews headed in that direction to deviate well north or south around the area of precipitation. The captain then requested to proceed direct to TXC, MTU, then as filed, per the dispatcher's suggested routing around the weather. The controller cleared the flight as requested, and at 0143, instructed them to contact the Denver ARTCC (ZDV). 

About 0143, the captain contacted ZDV and asked about the approaching weather and if any other flights had gone through it or if they had deviated north or south to get around it. According to the captain, the ZDV controller advised upon check in that the sector had just opened up, and the captain stated he believed that indicated that the weather might have been improving. The ZDV controller did not provide the weather conditions but advised the flight crew of a "hole," or gap, in the weather, which was on about a 240 to 245-degree heading that he felt they could get through with some deviations.

About 0154, the pilot of eastbound Southwest Airlines flight 3318, which had just passed through the hole in the weather in the opposite direction, provided a pilot weather report (PIREP) to the ZDV controller indicating that the hole was starting to close and that he did not think anybody should go through it behind them. The ZDV controller did not provide this PIREP to the incident flight crew. Also about 0154, as the incident flight was about 50 to 60 miles from the weather, the pilot of eastbound American Airlines flight 1155, which had passed the incident flight earlier in the opposite direction, reported a dramatic temperature increase at cruise altitude. According to the incident captain, he also noted a temperature increase at cruise altitude, followed by a "rough ride" and "static discharge," and he briefly could not hear the radio due to the static. 

At 0200:42, the captain informed the ZDV controller that he wanted to turn around and requested a southerly heading. The ZDV controller instructed the flight to turn left to a heading of 115°. At 0201:11, the ZDV controller advised the captain that he was turning toward a cell to the south and asked him to let him know if that was not going to work.

According to flight crewmember interviews, about 0202, as the they turned the airplane left, the weather radar display began to indicate red. The flight crew chose to turn right, and the flight subsequently encountered hail, which shattered the outside panes of both of the airplane's forward windows. The captain declared an emergency, and due to the noise associated with the hail striking the airplane and windshield, assumed the PF duties and began a descent to FL230. The flight crew diverted the airplane to DEN, landed at 0242, and arrived at the gate at 0255.




DAMAGE TO AIRCRAFT

In addition to the windshield damage, the airframe sustained minor hail impact damage. Although the outer windshield was completely shattered, the seal between the interior of the airplane and the outside atmosphere was not broken. The wings' leading edges, engine cowlings, parts of the aircraft skin, and especially the aircraft nose cone, or radome, sustained surface damage. The nose cone damage also resulted in damage to the airborne weather radar antenna, which rendered the system unusable after the flight encountered the hail.

PERSONNEL INFORMATION

The flight crew consisted of two pilots and three flight attendants. The flight crew was based in Minneapolis, St. Paul, Minnesota. The incident occurred during the first leg of the third day of a four-day pairing.

The captain, age 57, held a valid Federal Aviation Administration (FAA) airline transport pilot (ATP) certificate with a type rating for the Airbus A320. The captain held a first-class medical certificate with a limitation to have glasses for near vision, and he had his glasses for the incident flight. 

The captain was originally hired by Northwest Airlines in January 1989. He had been an Airbus captain for about 11 years. According to Delta Air Lines, his total flight time was 16,628 hours, 13,846 hours of which were in Airbus airplanes and 5,818 hours of which were as pilot-in-command. 

The first officer, age 44, held a current ATP certificate with a type rating for the A320. The first officer held a first-class medical certificate with a limitation to wear glasses, and he was wearing his glasses during the incident flight.

The first officer was originally hired by Northwest Air Lines on October 30, 2000. He had been flying the A319/320 for about 4 years. According to Delta Air Lines, his total flight time was 4.682 hours, 922 hours of which were in Airbus airplanes.

The assigned flight dispatcher was originally hired by Delta Air Lines on September 27, 1977. He began working for Delta Air Lines cleaning airplanes before eventually pursuing training and placement as a flight dispatcher and had been certified for more than 30 years.

The ZDV air traffic controller was originally hired by the FAA in July 2011. After completing initial ATC training, he was assigned to ZDV and was certified in January 2015 on the radar position he was working at the time of the incident.

A review of the FAA Program Tracking and Reporting Subsystem (PTRS) database showed no records or reports of any previous aviation incidents or accidents involving the captain or first officer.

AIRCRAFT INFORMATION

According to FAA records, the incident airplane was an A320-211, registration number N332NW, serial number 319, registered to Delta Air Lines. The airplane was powered by two CFM56-5A1 engines. At the time of the incident, the airplane logbook contained one deferred item for the auxiliary power unit. The airplane was dispatched with a maximum landing weight of 142,198 pounds, and it landed at DEN with an estimated weight of 130,718 pounds.

METEOROLOGICAL INFORMATION

The National Weather Service (NWS) issued a severe thunderstorm watch for the incident site and surrounding area at 2105 with severe weather possible through 0500. Further, the NWS issued a severe thunderstorm warning for the area north of the airplane's flightpath as early as 0133, at which time the incident aircraft was still in ZMP airspace about 230 miles east-northeast of the developing thunderstorms they later encountered. The NWS Storm Prediction Center (SPC) day 1 convective outlook that was issued and valid before the incident flight crew received their preflight weather information forecast areas of severe weather along the flight route. The NWS area forecast issued before the incident flight received their preflight weather information also mentioned thunderstorms, possibly severe, along the flight route. Neither the NWS SPC day 1 convective outlook nor the area forecast were provided to the incident flight crew. As noted, the preflight weather briefing sent to the incident flight crew by the company dispatcher noted that there was a chance of afternoon thunderstorms around the destination airport, but it did not mention thunderstorm activity along the flight route until near the destination.

Title 14 CFR 121.601(c) requires dispatchers to provide the pilot-in-command (PIC) any additional available information of meteorological conditions (including adverse weather phenomena, such as clear air turbulence, thunderstorms, and low altitude wind shear) during the flight. Delta Air Lines Flight Control Operations Manual (FCOM) reiterates the content of the CFR and further outlines the criticality of the dispatchers constant vigilance of significant meteorological events and requirements for use of TPs. For more detailed information, see the "Relevant Procedures" section of this report.

When asked about NWS products, and why he had not provided that information in the preflight weather information, he said that he generally did not use NWS products because the products from his company meteorology department were more accurate and reliable.

The NWS surface analysis chart for 0300 depicted a stationary front just south of the incident site located in northwestern Kansas with thunderstorms and rain reported in the two surface stations near the incident site.

Cheyenne County Municipal Airport (SYF), located 24 miles southwest of the incident location, was the closest official surface weather station to the incident site. The 0155 SYF surface observation reported wind from 180° at 10 knots with gusts to 19 knots, 10 miles visibility, clear skies below 12,000 ft above ground level, temperature of 31° C, dew point temperature of 11° C, and an altimeter setting of 29.75 inches of mercury. Remarks: automated station with precipitation discriminator, temperature 30.5° C, dew point temperature 10.9° C.

Imperial Municipal Airport (IML), located 29 miles north-northwest of the incident location. Although SYF was located physically closer to the incident location, the thunderstorm line was not located above SYF at 0155; however, at the time of the incident, the thunderstorm line was over IML; therefore, the 0201 weather observation from IML would have been more representative of the conditions the incident flight crew encountered during the incident. The IML surface observation at 0201 reported wind from 230° at 14 knots, thunderstorms, temperature of 22° C, dew point temperature of 19° C, altimeter setting of 29.90 inches of mercury. Remarks: automated station with precipitation discriminator, lightning distant all quadrants, temperature 21.7° C, dew point temperature 18.9° C, present weather identifier sensor is not operating, maintenance is needed on the system.

SIGMETs 1C and 5C were valid for the area surrounding the incident site at the time of the incident. SIGMET 1C was issued at 0055 (valid through 0255) and SIGMET 5C was issued at 0155 (valid through 0355) and both warned of thunderstorm activity along the route of flight. SIGMET 1C warned of areas of severe thunderstorms moving from 250° at 30 knots with thunderstorms tops above FL450. Tornadoes, hail to 2 inches, and wind gusts to 60 knots were all possible in the severe thunderstorms discussed in SIGMET 1C. SIGMET 5C warned of areas of severe thunderstorms moving from 250° at 30 knots with thunderstorm tops above FL450. Tornadoes, hail to 2 inches, and wind gusts up to 60 knots were all possible in the severe thunderstorms discussed in SIGMET 5C.

In addition, Delta Air Lines Meteorology issued TPs for thunderstorm activity (including along the incident aircraft's route of flight) at 0113 (TP CN12) and 0159 (TP CN13); however, neither TP CN12 or CN13 were sent to the incident flight crew. The dispatcher did send TP CN11, which was issued at 0049, to the incident flight at 0138, but TP CN11 did not contain information about thunderstorm activity along the flight route. As mentioned earlier, 14 CFR Part 121.601 would also apply here with regards to the requirement of the flight dispatcher to provide the PIC with additional meteorological information. 

Composite reflectivity is the weather radar data that goes into the ATC weather and radar processor (WARP). The weather is displayed via WARP for a view of weather targets on the controller's radar display at ARTCCs and was viewable by the ZDV controller. Composite reflectivity is also the weather radar data that goes into the weather radar information available at the Delta OCC and was viewable by the company dispatcher. The imagery is available to the user after all of the elevations scans from the weather surveillance radar-88D are complete, which takes about 5 to 6 minutes. 

Delta Air Lines pilots are required to maintain a lateral distance of 20 miles between individual thunderstorms when operating above 25,000 ft. A review of the composite reflectivity image that started at 0133 and was available to ZDV and Delta OCC at 0138 showed that the total gap distance between the areas of thunderstorm activity was 30 miles. The 0138 the composite reflectivity image, which was available to ZDV and Delta OCC at 0143, showed that the total gap distance between the areas of thunderstorm activity had reduced to 26 miles. The 0143 the composite reflectivity image, which was available to ZDV and Delta OCC at 0149, showed that the total gap distance between the areas of thunderstorm activity had reduced to 23 miles with the incident airplane between about 80 and 100 miles east-northeast of the thunderstorm activity. The 0149 composite reflectivity image, which was available to ZDV and Delta OCC at 0149, showed that the total gap distance between the areas of thunderstorm activity had reduced to 12 miles with the incident airplane about 55 to 75 miles east-northeast of the incident site. The 0153 composite reflectivity image, which was available to ZDV and Delta OCC at 0158, showed that the total gap distance had reduced to 9 miles between areas of thunderstorm activity with the incident airplane about 30 to 40 miles east-northeast of the incident site. Composite reflectivity images starting at 0158 and 0203, which were available to ZDV and Delta OCC at 0203 and 0207, respectively, showed that the total gap distance between thunderstorm activity had reduced to 7 and 4 miles, respectively. 

COMMUNICATIONS

A review of ATC audio from ZMP revealed that the incident flight crew was initially advised of the impending weather, which they ultimately encountered, while the flight was more than 130 miles away from it. Additionally, the ZMP controller also reported to the incident flight crew that several other aircraft were deviating either north or south around the weather. The company dispatcher subsequently sent the flight crew an alternate routing. The ZMP controller subsequently cleared flight 1889 via the dispatch-assigned alternate routing as requested and transferred communications to ZDV.

Upon checking in with ZDV at 0143, the captain immediately asked about the weather ahead; however, according to information provided in postincident interviews, the ZDV controller did not issue known weather information as required by FAA Order JO 7110.65, "Air Traffic Control," because he felt the pilot was already aware of the weather since he had asked about it when checking in. However, the ZDV controller did attempt to assist the flight crew in attempting to navigate through a gap in the weather.

About 20 minutes after the flight crew initially checked in with ZDV, the flight penetrated the thunderstorm and encountered hail. During this time, the captain made several attempts to get more detailed information from the ZDV controller about flight conditions within the hole through which they were attempting to pass. At 0154, the ZDV controller solicited a PIREP from Southwest Airlines flight 3318, which had just passed through the hole in the opposite direction. The PIREP noted that the hole was continuing to close and that nobody should go through behind them; however, the controller did not provide the PIREP to the incident flight crew. 

FLIGHT RECORDERS

The cockpit voice recorder from the incident airplane had already been removed, placed into service in another airplane, and overwritten before a decision was made to conduct the investigation.

The data from the airplane's flight data recorder were downloaded and provided in an electronic file to the National Transportation Safety Board. The file contained about 66 hours of data. 

MEDICAL AND PATHOLOGICAL INFORMATION

Neither the captain or first officer received, nor were they required to receive, drug and alcohol screening as a result of this incident. 

ADDITIONAL INFORMATION

Relevant Procedures

According to the Delta Air Lines Airway Manual, page SUP-4, page WX.2.19, a severe thunderstorm was defined as one with 50 knots or greater wind gusts, hail 1 inch or larger, or a tornado. As a general rule, severe thunderstorms had distinct characteristics and/or signatures that make them relatively easy to identify including the following: 

Severe thunderstorms generally were found in lines. They could occur in isolated form, but less frequently. Squall lines usually formed ahead of fast-moving cold fronts. They could also form along a trough, a convergence zone, or a frontal wave. Squall lines usually were formed and were generally oriented along a northeast/southwest line. As they grew in length, they most often extended further to the southwest. This southwestward growth could be very rapid.

According to the captain, they first heard about the weather along their route from ATC when they were about 150 miles away from the line of weather and began observing the weather displayed on their navigational display.

According to the Delta Air Lines Airway Manual, "Weather – Hazardous Weather" (page Ops-4WX.2.2), any flight in the vicinity of thunderstorms carried the risk of a sudden onset of moderate or severe turbulence. All efforts should be made to avoid thunderstorm penetration whenever possible. The Delta Air Lines Airway Manual further stated that pilots "do not operate through an area of thunderstorms unless separations between individual thunderstorms cells are the following minimum distances:

5 miles – Below 10,000 feet 

10 miles – Between 10,000 and 25,000 feet 

20 miles – At or above 25,000.

In addition, the Delta Air Lines Airway Manual, Weather – Hazardous Weather (page Ops-4WX.2.2 – 2.3), stated: 

Enroute deviations should be made upwind of the storm when possible, especially if winds aloft are strong. Deviating downwind greatly increase the chance of encountering hail and turbulence. 

Caution: Turbulence can be expected downwind of the storm 1 NM for every knot of wind speed at flight altitude. 

- Avoid flight under the anvil. The greatest possibility of encountering hail is downwind of the cell, where hail falls from the anvil or is tossed out from the side of the storm. 

- Avoid cirrus and cirrostratus layers downwind from the storm tops. Such layers may be formed by cumulonimbus tops and may contain hail, even though the radar shows little or no return echoes.

Caution: Hail has been encountered as much as 20 NM downwind from large thunderstorms.

According to the Delta Air Lines A319/320 Operations Manual, page SP.11.20, pilots should plan a weather deviation path early, and simply skirting the areas of intense thunderstorm activity may not be enough to avoid the weather. Weather echoes that appeared beyond 100 miles should be considered strong. The following steps were provided as guidance to assist the pilot when interrogating potential weather hazards: 

- Set RANGE to either 80 or 160 NM. 

- Adjust the TILT until the ground appears in the upper third of the display. 

- Adjust the GAIN control as follows depending on the aircraft altitude: 

> FL250 use the MIN through MAX 

< FL250 leave the GAIN in CAL

The Delta Air Lines A319/320 Operations Manual stated that, when viewing the short ranges, pilots should avoid flying into a "box canyon" by periodically switching to longer range displays to observe distant conditions. When deviating around thunderstorms at higher altitudes, pilots should avoid the "blowoff" that may produce significant turbulence, and avoid deviating around the downwind side of large thunderstorms. When that was not possible, pilots should stay at least 1 mile downwind from the return for every knot of wind (for example, if the wind is 50 knots, deviate at least 50 miles to the downwind side).

Title 14 CFR Part 121.601 stated the following about aircraft dispatcher information required to be provided to the PIC:

(a) The aircraft dispatcher shall provide the pilot in command all available current reports or information on airport conditions and irregularities of navigation facilities that may affect the safety of the flight.

(b) Before beginning a flight, the aircraft dispatcher shall provide the pilot in command with all available weather reports and forecasts of weather phenomena that may affect the safety of flight, including adverse weather phenomena, such as clear air turbulence, thunderstorms, and low altitude wind shear, for each route to be flown and each airport to be used,

(c) During a flight, the aircraft dispatcher shall provide the pilot in command any additional available information of meteorological conditions (including adverse weather phenomena, such as clear air turbulence, thunderstorms, and low altitude wind shear), and irregularities of facilities and services that may affect the safety of the flight.

FAA Order JO 7110.65, Air Traffic Control, page 2-6-1, paragraph 2-6-1, outlined the requirements for air traffic controllers to provide known weather information to the pilot and stated, in part, the following:

Become familiar with pertinent weather information when coming on duty, and stay aware of current weather information needed to perform ATC duties.

In addition, FAA Order JO 7110.65, page 2-6-1, section 2-6-2, also stated the following:

Controllers must advise pilots of hazardous weather that may impact operations within 150 NM of their sector or area of jurisdiction. Hazardous weather information contained in HIWAS broadcasts includes Airmen's Meteorological Information (AIRMET), Significant Meteorological Information (SIGMET), Convective SIGMET (WST), Urgent Pilot Weather Reports (UUA), and Center Weather Advisories (CWA).

FAA Order JO 7110.65, page 2-6-1 and 2-6-2, section 2-6-3, stated, in part, the following regarding significant PIREP information and air traffic controller requirements to disseminate this information to pilots:

Significant PIREP information includes reports of strong frontal activity, squall lines, thunderstorms, light to severe icing, wind shear and turbulence (including clear air turbulence) of moderate or greater intensity, volcanic eruptions and volcanic ash clouds, detection of sulfur gases (SO2 or H2S) in the cabin, and other conditions pertinent to flight safety.

a. Solicit PIREPs when requested or when one of the following conditions exists or is forecast for your area of jurisdiction:

1. Ceilings at or below 5,000 feet. These PIREPs must include cloud base/top reports when feasible.

2. Visibility (surface or aloft) at or less than 5 miles.

3. Thunderstorms and related phenomena.

4. Turbulence of moderate degree or greater.

5. Icing of light degree or greater.

6. Wind shear.

d. Handle PIREPs as follows:

1. Relay pertinent PIREP information to concerned aircraft in a timely manner.

2. En Route. Relay all operationally significant PIREPs to the facility weather coordinator. 

FAA Order JO 7110.65, pages 2-6-2 through 2-6-4, section 2-6-4, stated, in part, the following regarding air traffic controller requirements to issue pertinent weather information to pilots:

a. Issue pertinent information on observed/reported weather and chaff areas by defining the area of coverage in terms of azimuth (by referring to the 12-hour clock) and distance from the aircraft or by indicating the general width of the area and the area of coverage in terms of fixes or distance and direction from fixes.

Note -Weather significant to the safety of aircraft includes such conditions as funnel cloud activity, lines of thunderstorms, embedded thunderstorms, large hail, wind shear, microbursts, moderate to extreme turbulence (including CAT), and light to severe icing.

c. Use the term "precipitation" when describing radar-derived weather. Issue the precipitation intensity from the lowest descriptor (LIGHT) to the highest descriptor (EXTREME) when that information is available. Do not use the word "turbulence" in describing radar-derived weather.

1. Light.

2. Moderate.

3. Heavy.

4. Extreme.

Note -Weather and Radar Processor (WARP) does not display light intensity.

g. When requested by the pilot, provide radar navigational guidance and/or approve deviations around weather or chaff areas. In areas of significant weather, plan ahead and be prepared to suggest, upon pilot request, the use of alternative routes/altitudes.

1. An approval for lateral deviation authorizes the pilot to maneuver left or right within the limits of the lateral deviation area.

2. If a pilot enters your area of jurisdiction already deviating for weather, advise the pilot of any additional pertinent weather which may affect his route.

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