Narrative:

FAA is installing 'improved' low level wind shear alert system (LLWAS) at many airports nationwide. It uses much of the existing equipment from the old LLWAS system; however, it's designed to detect wind shear in the vicinity of the center field sensor, as well as around the airport periphery. The improved system uses an algorithm to calculate wind shear amongst the various sensors, whereas the old system only compared each boundary wind to the center field wind. Old LLWAS readout in tower showed a center field wind and 5 boundary winds. Improved LLWAS uses the old equipment; however, the new system contains 2 center field wind indications--one based on a 2 min average and the other based on a 30 second average. Therefore, although there are still 5 boundary sensors, only 4 can be read out and the fifth is called 'hidden sensor.' the information from this sensor is used by the system to compute wind shear, but information from this sensor is not available to controllers or pilots because of money and logistics--too expensive to add the extra line and updated readout equipment. Problem with system became obvious the first week it was installed. LLWAS would alarm and we'd issue wind shear alerts for 10 degrees or a couple of KTS. Old LLWAS system would alarm only if it detected any variation of velocity/direction to equal or exceed a 45 degree vector difference. Also, if system detects wind shear in vicinity of center field sensor, we must broadcast: 'wind shear alert, center field wind (direction) at (velocity) varying to (direction) at (velocity,) reading both the 2 min and 30 second averages. We have seen the center field sensor alarm with exactly the same wind direction and velocity showing from both readouts. Since we were reluctant to broadcast a variance of exactly 0, we questioned the accuracy of the system. Arwy facs and the folks at okc swear it is working as intended. I am concerned that this system is providing misleading information to pilots about possible wind shear during critical phases of flight. The system would not alarm unless some potentially seriouswind shear was taking place, but because the hidden sensor information is not available to us, all we can issue is the other wind information. For instance, let's say the winds are: center field-050/07, northeast boundary-050/08, northwest boundary-040/06, southwest boundary-100/08, southeast boundary-120/09 (hidden sensor-180/15). This is not exact, since I'm unfamiliar with the algorithm required, but we see this type of situation happen often. The system may alarm, but the readouts which flash will be, say, the center field, northeast boundary and northwest boundary, and these are what we must issue to pilots. With this information, we can only assume that the sensor which is causing the alarm is the hidden sensor, although we do not have this information (the readout I have provided is for the sake of argument). My point is that this type of wind may exist at the hidden sensor, indicating possible serious wind shear, but the information isn't available. All we can issue is wind information which may only be varying by a few degrees or KTS, and we are required by FAA 7110.65 to issue this information. My point is that a general wind shear warning to pilots may be more useful and less misleading than to tell them that the wind is varying only slightly. I do not believe the installation of this system is being made known to pilots. At least if they had a heads-up on it they would know to expect possible shears of greater magnitude than we are able to issue. Why the FAA seems to be keeping this a secret is a mystery to me. This system is being installed in at least 50 airports around the country, perhaps twice that many. My purpose in filing this report is to try to get the word out. The system is improved in that it will alarm more often and detect more shears, but I feel it is a danger because it does not provide useful information which should be available to pilots, and it is potentially misleading in the omission of that information. Callback conversation with reporter revealed the following: reporter states that equipment appears to be working better now. Still concerned that the hidden sensor is not indicated on the readout display in the tower. No ucr has been filed. Facility manager has checked into reporter's concern and found out that new LLWAS is operating as designed. The readout equipment in the cabin is the same as the old LLWAS. Reporter still feels that they are not getting all the information and would like to see the hidden sensor also displayed. Not sure if the hidden sensor is one of the center field sensors or boundary sensors. Cost of replacing equipment in tower may be one of the considerations in not changing display unit in cabin. Reporter states that nuisance alarms are not a problem, but thinks that pilots aren't getting all the information.

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Original NASA ASRS Text

Title: CTLR REPORTER STATES THAT NEW LOW LEVEL WIND SHEAR ALERT SYSTEM (LLWAS) DOES NOT GIVEN INDICATION OF FIFTH SENSOR ON TWR MONITOR PANEL. BELIEVES THAT INFORMATION MAY BE USEFUL TO PLTS.

Narrative: FAA IS INSTALLING 'IMPROVED' LOW LEVEL WIND SHEAR ALERT SYS (LLWAS) AT MANY ARPTS NATIONWIDE. IT USES MUCH OF THE EXISTING EQUIP FROM THE OLD LLWAS SYS; HOWEVER, IT'S DESIGNED TO DETECT WIND SHEAR IN THE VICINITY OF THE CENTER FIELD SENSOR, AS WELL AS AROUND THE ARPT PERIPHERY. THE IMPROVED SYS USES AN ALGORITHM TO CALCULATE WIND SHEAR AMONGST THE VARIOUS SENSORS, WHEREAS THE OLD SYS ONLY COMPARED EACH BOUNDARY WIND TO THE CENTER FIELD WIND. OLD LLWAS READOUT IN TWR SHOWED A CENTER FIELD WIND AND 5 BOUNDARY WINDS. IMPROVED LLWAS USES THE OLD EQUIP; HOWEVER, THE NEW SYS CONTAINS 2 CENTER FIELD WIND INDICATIONS--ONE BASED ON A 2 MIN AVERAGE AND THE OTHER BASED ON A 30 SEC AVERAGE. THEREFORE, ALTHOUGH THERE ARE STILL 5 BOUNDARY SENSORS, ONLY 4 CAN BE READ OUT AND THE FIFTH IS CALLED 'HIDDEN SENSOR.' THE INFO FROM THIS SENSOR IS USED BY THE SYS TO COMPUTE WIND SHEAR, BUT INFO FROM THIS SENSOR IS NOT AVAILABLE TO CTLRS OR PLTS BECAUSE OF MONEY AND LOGISTICS--TOO EXPENSIVE TO ADD THE EXTRA LINE AND UPDATED READOUT EQUIP. PROB WITH SYS BECAME OBVIOUS THE FIRST WK IT WAS INSTALLED. LLWAS WOULD ALARM AND WE'D ISSUE WIND SHEAR ALERTS FOR 10 DEGS OR A COUPLE OF KTS. OLD LLWAS SYS WOULD ALARM ONLY IF IT DETECTED ANY VARIATION OF VELOCITY/DIRECTION TO EQUAL OR EXCEED A 45 DEG VECTOR DIFFERENCE. ALSO, IF SYS DETECTS WIND SHEAR IN VICINITY OF CENTER FIELD SENSOR, WE MUST BROADCAST: 'WIND SHEAR ALERT, CENTER FIELD WIND (DIRECTION) AT (VELOCITY) VARYING TO (DIRECTION) AT (VELOCITY,) READING BOTH THE 2 MIN AND 30 SEC AVERAGES. WE HAVE SEEN THE CENTER FIELD SENSOR ALARM WITH EXACTLY THE SAME WIND DIRECTION AND VELOCITY SHOWING FROM BOTH READOUTS. SINCE WE WERE RELUCTANT TO BROADCAST A VARIANCE OF EXACTLY 0, WE QUESTIONED THE ACCURACY OF THE SYS. ARWY FACS AND THE FOLKS AT OKC SWEAR IT IS WORKING AS INTENDED. I AM CONCERNED THAT THIS SYS IS PROVIDING MISLEADING INFO TO PLTS ABOUT POSSIBLE WIND SHEAR DURING CRITICAL PHASES OF FLT. THE SYS WOULD NOT ALARM UNLESS SOME POTENTIALLY SERIOUSWIND SHEAR WAS TAKING PLACE, BUT BECAUSE THE HIDDEN SENSOR INFO IS NOT AVAILABLE TO US, ALL WE CAN ISSUE IS THE OTHER WIND INFO. FOR INSTANCE, LET'S SAY THE WINDS ARE: CENTER FIELD-050/07, NE BOUNDARY-050/08, NW BOUNDARY-040/06, SW BOUNDARY-100/08, SE BOUNDARY-120/09 (HIDDEN SENSOR-180/15). THIS IS NOT EXACT, SINCE I'M UNFAMILIAR WITH THE ALGORITHM REQUIRED, BUT WE SEE THIS TYPE OF SITUATION HAPPEN OFTEN. THE SYS MAY ALARM, BUT THE READOUTS WHICH FLASH WILL BE, SAY, THE CENTER FIELD, NE BOUNDARY AND NW BOUNDARY, AND THESE ARE WHAT WE MUST ISSUE TO PLTS. WITH THIS INFO, WE CAN ONLY ASSUME THAT THE SENSOR WHICH IS CAUSING THE ALARM IS THE HIDDEN SENSOR, ALTHOUGH WE DO NOT HAVE THIS INFO (THE READOUT I HAVE PROVIDED IS FOR THE SAKE OF ARGUMENT). MY POINT IS THAT THIS TYPE OF WIND MAY EXIST AT THE HIDDEN SENSOR, INDICATING POSSIBLE SERIOUS WIND SHEAR, BUT THE INFO ISN'T AVAILABLE. ALL WE CAN ISSUE IS WIND INFO WHICH MAY ONLY BE VARYING BY A FEW DEGS OR KTS, AND WE ARE REQUIRED BY FAA 7110.65 TO ISSUE THIS INFO. MY POINT IS THAT A GENERAL WIND SHEAR WARNING TO PLTS MAY BE MORE USEFUL AND LESS MISLEADING THAN TO TELL THEM THAT THE WIND IS VARYING ONLY SLIGHTLY. I DO NOT BELIEVE THE INSTALLATION OF THIS SYS IS BEING MADE KNOWN TO PLTS. AT LEAST IF THEY HAD A HEADS-UP ON IT THEY WOULD KNOW TO EXPECT POSSIBLE SHEARS OF GREATER MAGNITUDE THAN WE ARE ABLE TO ISSUE. WHY THE FAA SEEMS TO BE KEEPING THIS A SECRET IS A MYSTERY TO ME. THIS SYS IS BEING INSTALLED IN AT LEAST 50 ARPTS AROUND THE COUNTRY, PERHAPS TWICE THAT MANY. MY PURPOSE IN FILING THIS RPT IS TO TRY TO GET THE WORD OUT. THE SYS IS IMPROVED IN THAT IT WILL ALARM MORE OFTEN AND DETECT MORE SHEARS, BUT I FEEL IT IS A DANGER BECAUSE IT DOES NOT PROVIDE USEFUL INFO WHICH SHOULD BE AVAILABLE TO PLTS, AND IT IS POTENTIALLY MISLEADING IN THE OMISSION OF THAT INFO. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES THAT EQUIP APPEARS TO BE WORKING BETTER NOW. STILL CONCERNED THAT THE HIDDEN SENSOR IS NOT INDICATED ON THE READOUT DISPLAY IN THE TWR. NO UCR HAS BEEN FILED. FAC MGR HAS CHKED INTO RPTR'S CONCERN AND FOUND OUT THAT NEW LLWAS IS OPERATING AS DESIGNED. THE READOUT EQUIP IN THE CABIN IS THE SAME AS THE OLD LLWAS. RPTR STILL FEELS THAT THEY ARE NOT GETTING ALL THE INFO AND WOULD LIKE TO SEE THE HIDDEN SENSOR ALSO DISPLAYED. NOT SURE IF THE HIDDEN SENSOR IS ONE OF THE CENTER FIELD SENSORS OR BOUNDARY SENSORS. COST OF REPLACING EQUIP IN TWR MAY BE ONE OF THE CONSIDERATIONS IN NOT CHANGING DISPLAY UNIT IN CABIN. REPORTER STATES THAT NUISANCE ALARMS ARE NOT A PROB, BUT THINKS THAT PLTS AREN'T GETTING ALL THE INFO.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.