Blow Hard

anemometersJulian Green reports on an innovative US wind profiling initiative at Juneau Airport.

Turbulence around Juneau Airport, Alaska is legendary.

As Ken Williams, senior captain with Alaska Airlines described the flying environment: “Flying into Alaska’s capital city can be very challenging. The complexity of the local terrain and how it creates four unique wind patterns that can generate severe mechanical turbulence at times, provide pilots with very tough challenges.”

Juneau Airport sits at the end of the Gastineau Channel, surrounded by steeply rising mountains. The area experiences extreme winds streaming into and over the narrow channel in NNE and SE directions, with the exact direction and speed of the winds interacting with the mountains and valleys determining how strong the turbulence will be and where it will be located.

The combination of weather and topography presents uniquely complex operational challenges that cause severe disruption often for days at a time. In one case they forced the skilled crew of a departing Alaska Airlines 737 to recover the aircraft a mere 150 feet from the ground after a massive gust caused it to bank more than 90 degrees.

That incident in January 1993 caused authorities and Alaska Airlines to reconsider the safety parameters for the airport. As a consequence, the Federal Aviation Administration (FAA) closed the affected Lemon Creek and Fox departure routes, severely limiting operations at Juneau during adverse weather between September and May.

LEAD-IMAGE-juneau-airportAs Ken Williams describes: “A FAA report to Congress on the safety of Juneau Airport set in motion direct scrutiny of our departure procedures in Juneau to the point where we actually lost our operating specification during the summer and autumn of 1996.  We could deliver passengers to Juneau during strong SE wind events, but we had to ferry the aircraft out empty.” It presented the airline with a major commercial impediment especially since Juneau is Alaska Airlines’ operational hub.

The events also caused other airlines including Delta, Evergreen and Mark Air to abandon services to Juneau, which is the only US state capital inaccessible by road and relies almost exclusively on air services for its economic sustainability.

While a temporary set of rules was put in place so departure routes could be reopened, a longer term solution was needed that would alert pilots to turbulence in the airport environment. In 1995, Alaska Airlines’ senior operational personnel launched the Juneau Anemometer Project. With the support of a local senator who secured federal funding, the National Center for Atmospheric Research (NCAR) was engaged to develop a system that would improve the reliability and safety of aircraft movements in the longer term.

Al Yates, current project leader at the NCAR for what was to become JAWS – or Juneau Airport Winds System – explained to Air Traffic Management that there was no commercial off-the-shelf system that would solve the problem.

“The turbulence around Juneau International Airport is primarily mechanical in nature in that it’s based on the interaction of winds and terrain, and does not involve convective heating.  It is therefore unique and requires a solution based upon Juneau-specific data. Because NCAR had recently developed a turbulence alerting system for Hong Kong Airport which had similar turbulence issues, the FAA requested help in developing a system for Juneau,” says Yates.


It was a long gestation, one complicated by the terrain, severity of conditions and complicated approach and departure profiles, as well as the need to maintain operations.

“Part of the temporary solution put in place by the FAA involved Alaska Airlines installing wind sensors in various locations around the airport. NCAR installed additional sensors to capture wind information in the area.”

Field tests were conducted where aircraft were flown during all types of weather, ‘but the worse the better’ as Yates says, in an effort to gather turbulence information.

JAWS-Alert-Display“To develop a statistical basis for the alert system, data was collected from wind sensors and a dedicated aircraft made turbulence measurements flying throughout the Juneau airspace. Flights were conducted in benign, moderate, and especially rough conditions to sample the full range of conditions.”

Information from aircraft was augmented with Doppler radar data and was mapped with hot spots pinpointed. Then came a lengthy process correlating wind information gathered by the installed sensors with turbulence information gathered by aircraft.

“Because of the mechanical nature of the turbulence, correlations were high and repeatable,” says Yates. “The best sets of correlations were used in software that was developed to infer the turbulence in near-real time and display it in a manner easily understood by dispatchers and pilots.”

This was the genesis of JAWS, a system that was progressively developed to a point where it was subsequently delivered to the FAA for further refinement with the objective of ongoing operational use in Juneau.

“The FAA developed their end-state system – JAWS-E – based on modifications to the NCAR prototype system and installed the modifications in Juneau,” Yates explains.

“The NCAR prototype and the FAA end-state system were operated in parallel for several months to validate operation of the FAA system, to ensure results from the FAA system matched those from the NCAR prototype within acceptable tolerances.”

Yates says the NCAR prototype was turned off when the FAA determined its system was operating in an acceptable manner. In January 2012, the FAA system took over providing turbulence information.


Yates adds that upon certification, the FAA determined the system had a 91 per cent probability of detecting moderate or greater turbulence.  “This far exceeded the FAA threshold for acceptable performance, which was a 60 per cent probability of detection.

“The NCAR prototype was never intended to remain in place indefinitely. The JAWS-E system was designed to be more cost-effective and efficient in terms of computer use and software architecture was modified to work on the reduced hardware footprint.”  All the sensors and sites operated by NCAR were transferred to the FAA and incorporated within JAWS-E.

JAWS-E essentially represents refinements to the gathering and display of information.

ScreenThe system has no predictive function. “Real-time data, received several times a minute, is analysed and generates appropriate alerts, while wind data is provided for the last hour, and trends may be evident from that historical data.”

For the contributing parties to the JAWS project – Alaska Airlines, the NCAR and the FAA together with local aviation authorities – the development of a system that was robust and reliable was key to successful implementation.

“The FAA told us they thought there may be as much as a 50 per cent increase in flights departing Juneau during the bad weather season,” Yates says with some satisfaction.

Williams, who has been part of the project since its inception in 1995, adds: “JAWS has provided aviation with a system that can boast that since its inception, not one aircraft has experienced a severe upset or severe turbulence encounter within the coverage of the JAWS system.

“This would never have been possible without the direct involvement of NCAR. We have been very impressed with all those from the NCAR team that helped make JAWS such a success story. The great depth of knowledge, leveraging the latest technologies and the unbelievable patience and doggedness in dealing with setback after setback due to weather, technical and other issues really tells the story of what one would want in a highly critical programme that enhances aviation safety,” says Williams.


“We use the JAWS alerting system 24/7 as a dispatch tool, approach and departure guidance as per FAA Operations Specifications and as a trend-monitoring tool as weather systems move through the Juneau airport basin.

“The FAA Flight Service Station personnel use the JAWS Alerting System for pilot briefings and the Juneau weather forecast office adjusts its forecast products with the wind profiler information provided by the JAWS integrated display. The JAWS alerts and wind information are delivered to the crews in flight via ACARS. Flight crews can also call any Alaska Airlines operations station in SE Alaska or the Juneau Flight Service Station for real time updates,” Williams explains.

The FAA and Alaska Airlines are even negotiating a new set of rules for flight operations in Juneau that use the output from JAWS-E as a determining operational factor.

juneau-airport2And while Alaska Airlines’ has been intimately involvement in the development of JAWS, the system is a safety benefit for all operators, whether commercial, freight or general aviation that together account for the nearly 90,000 aircraft movements Juneau airport accommodates each year.

“The City and Borough of Juneau like the system. However, economic factors will dictate whether other airlines make the decision to fly to Juneau,” explains Yates, adding that Alaska Airlines has incorporated Required Navigational Precision capable navigation systems across the airline’s fleet.

“That allows them to fly closer to terrain than most airlines can.  They have developed, with the support of the FAA, specialised RNP approach and departure procedures that utilise this specialised equipment, allowing them to fly their approach and departure patterns mostly in the clouds, because they have the required precision in their instruments to be able to avoid nearby terrain while flying in the clouds.

“Other airlines would have to implement the same solution in order to effectively fly into the Juneau area. Additionally, all Alaska Airlines pilots have been trained and undergo periodic refresher training so they can be certified to fly into Juneau.”

Williams concludes: “My colleagues and I hope the JAWS programme does not stop here. There is a real need for a similar system to be developed for Anchorage, Sitka, Reno, and Queenstown in New Zealand and other airports experiencing similar complex terrain induced turbulence.”

Posted in Features, Innovation, Meteorology

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