Weather Radar Techniques

[Dave Gwinn]

Holy Cow! Welcome aboard.:nana2:

Doug, can we get Mr. Gwinn his own section. I would have to say radar useage is the least taught and one of the most misunderstood items by pilots.

I'd be happy to participate in any way the group thinks would be most advantageous.

Incidentally, in the Delta 191 accident, Archie's analysis is badly flawed. They were never pointed AT that storm until final approach. IT was camouflaged by a dissapating storm in front of it. They were at LOW LEVEL and had no tilt capabilities to see what awaited them. AA#351 was asked if they could see the airport and replied: "When we get out of THIS RAINSHOWER we will." That was the last report Capt Connors heard. A big deal was made of the lighning strike. That was a FLASH 1.5 miles to the east of the approach course. The tower controllers saw NINE STRIKES ON THE SOUTH side of that storm and told no one. Capt Toler in Piedmont 70 stopped his plane so his crew could see: "I've seen squall lines before, but this was a monster. I wanted my crew to see it and couldn't believe they were landing planes through it." His wind shear began at 800' AGL. All wind shear training prior to that was Dr. John McCarthy, and his $499 training tape ENDED with "Remember, fellows, you HAVE to be BELOW 500'." He has immediately then amended UAL's FOP manual to state that wind shear can be entrapment at 1,000' and below.
Capt Connors had refused a South arrival, because "we're not tangling with thunderstorms" and was given a holding pattern at SHV for 23 minutes. On the Blue Ridge arrival with vectors, he was never pointed at that storm until he was committed to the approach. He had a 31 yr flawless career, nine type ratings, and a line checkman on 3 heavies. His F/O and F/E were training center instructors.
Archie was dismissed as a witness against the pilots due to some material in his course notes, and a video tape he made for Southwest, in which he said: "I know that you've done what I've done when there's a storm in the area and the airplane hasn't been washed lately. You fly back and forth beneath it to get a clean airplane."
I have refused many cases as a witness against pilots and airlines. I'll defend them, but never appear against them.

 

[wheelsup]

Re: Weather WX Techniques

Dave,

This article (page 15), put out by Honeywell in 2005, now says aim the tilt at 5,000'-15,000'. What do you recommend as an altitude to gauge the correct level of convection? If you tilt too low, heavy rain returns level 3 or 4 and you end punching thru and everything is fine. While it may be a level 3-4 return, it isn't what people correlate to level 3-4 returns in the fact that it's not convective. I think that leads to a "boy cries wolf" scenario where pilots at my company are flying thru level 3-4 paints and just saying that the radar "overpaints" and that it's OK. I fear that one of these days there are going to bust thru a true level 4 storm on approach and get the %#@% kicked out of them, thinking it was just heavy rain.

Thoughts?

 

[Dave Gwinn]

Hi, Matt:
Yeah, it gets kind of wacky, doesn't it. I don't know the gentleman whose name appears on that 'course', but it was developed by Steve Sweet in Radar Engineering. At the time, I had traveled to 4 continents and 15 countries to teach Airborne Wx Radar Seminars for "Honeywell Systems Training". When this 'course' came out, we simply said: WHY? Steve's first slide lists all of the radars he helped develop and the last statement is "A Radar Guy", but he is NOT a pilot. Frankly, I find the images complex, confusing, too cluttered and some areas not applicable to airborne operations.
I'm about ready for a saliva test with this Level I-II-III-IV confusion. If you look at the blue book Aviation Weather Services AC-45, you'll find there are those levels listed for BOTH stratus and convection rainfall rates, and not an explanation of who is using what rainfall rate.
It's my opinion they should be abandoned in all FOPs for avoiding "Convective Yellow", "Convective Red" and to treat Magenta anytime as a Severe Storm. A responsible pre-flt examination of the destination (Convective Outlook, etc) alerts one to the probability of thunderstorms. Coming down from altitude permits the pilot to observe any building Cu or towering clouds. (ATIS, by the way, when stating 'heavy rain' is, in their definition .3" per hour. "Yellow" on your radar.)
I understand the Centers will now refer to "light", "moderate", "heavy" or 'extreme' rainfall rates, and not Levels.
My advice (although you didn't say what aircraft you operate) is to put the beam one-half the beam-width up at FL180 when changing the altimeter (an 8 degree beam would be elevated to +4) which places the bottom of the beam level with the airplane and altitude. If there's no return at 18, and none at 12 and none at 7, then you're guaranteed it's low level rainshowers. Your radar is calibrated to stratus rainfall rates and one-half inch per hour triggers Red. Jeez, coming down from altitude can't you SEE the cloud formations surrounding the airport?
A long time ago I wrote an article wherein I relayed the experience of a regional carrier holding at the IAF because the airport was surrounded with Red, while a chap in a Baron (& Stormscope) saw no flashes and took the approach. He reported it was 'very wet and smooth'. Thereafter, the reg. carrier made an unremarkable approach.
At 15 miles from the airport on approach, tilt up 15 degrees. In a 3:1 descent profile, 15 miles out is about 4,500' AGL, and 15 degees up will provide excellent convective information at about the 8NM to 12NM areas. As you descend, the info will move to 12NM to 15NM, and as you commit to the approach, you get virtually 'convective blind'. At about 1,500' AGL over the LOM, and 15 degees up, the beam center is 9,000' above the airport. Good information, but still possible to be a thick layer of low level showers. The convective decision should have been made at 15NM or earlier.
With the new ASR-9 and ASR-11 approach radars (which are coordinated to the same rainfall rates as your radar) that is superb information out to 60 miles from the airport. Sitting on the ground for takeoff, you have the same problem: Tilt limited. Take off with 15 degrees up and you have a 'convective slice' at 10 to 15 miles from runway position. Again, the ASR-9 or ASR-11 (& Stormscope) are great supplements. You are virtually 'convectively blind' again, using your own radar for the first 10NM of takeoff and departure. At 10NM distance, go to the endorsed tilt sequence, which is to place the beam center between FL180 to FL250, but no higher. Personally, I like 180-to-220. (1) it affirms convection, (2) you see the affects of the 500mb winds on the echo (3) the color confirms the moisture available and a measure of the Updraft strength to hold that caliber of water suspended for you to view it.
I don't know of any way you can be aloft, and put the beam center at 5,000', and thereafter, interpret weather as opposed to the overwhelming ground returns that you will receive.
Is this any advantageous information for you, or do you need a more amplified explanation? Bravo for the Stormscope: No flashes, no thunderstorm (although building convection can enrich your dentist and still have not reached CB stage.)
Dave

 

[Dave Gwinn]

Re: Weather WX Techniques

Also, does anyone know what the NWS/NOAA "standard" thunderstorm is? I've got two different definitions, one from a manufacturer and one from an expert on the subject,

The NWS Standard Thunderstorm is a 3NM in diameter storm with a Red core. This was used for years to calibrate radar, when that storm was precisely beam filling. Honeywell still uses the 3NM storm, while Rockwell-Collins uses a 4NM storm in their 850 radar. Once 'inside' that beam filling area is where STC (Sensitivity Timing Control) functions, desensitizing the receiver, since one-half the distance is four times the reflectivity of a beam filling storm. So the storm is held stable in close by less sensitivity in the receiver.

 

[LGB]

New here on Jetcareers, not from the states but I do go there now and then. I fly mainly Asia, Europe and Middle East.

I found this forum when searching for information on weather radar use, so here are my additional questions:



1) Recently I discussed with other pilots whether or not (weather or not ...) a weather radar has any deterrent effect on birds. In other words, would you turn on your weather radar on a clear day, just to try to scare off these natures little flying machines, having no transponders, radios etc ... ? Not to expect one or two birds to make a significant echo large enough to spot them ... just to make them fly away from your path.

This leads to another question that I have not yet found an answer to.

2) How is the evolution of transmitted signal strength of conventional and more modern weather radar systems? With the introduction of phased planar array antennas as well as microprocessor/transistors, I know that the signal transmitted is now a lot lower than in classic systems. Safety distances for modern aircraft are often in the order of less than 20 feet (somewhat more for fueling operations) when operating the weather radar, while I seem to remember that more classic aircraft have a larger safety distance.

We operate a fleet of aircraft from different former operators, so we have different screens, some in B/W, some in colour. Some 74's we use even have color in one side, and B/W in the other - for the same picture!


Sorry, I have a few more questions now, leading from this.

3) Do you have any idea what radar beam width these typical 747 classic weather radar systems have? Cannot see it in the manual, so how can I find out?

4) Also, some pilots say that changing the range of the display also changes the strength or type of the beam. In this case, we have two screens for one radar - if one pilot sets 160 nm range while the other has 20 nm, which one decides the signal type then?

 

[Dave Gwinn]

1. I have no faith or any documented data to prove that radar prevents bird strikes. (In fact I took 28 sea gull strikes at DCA, 200' ceiling when a battalion of them left the Potomac River when they heard me 'cleared for takeoff' and flew right down the runway.....radar on.) In the olden days, perhaps 60,000 watt radars may have tickled them, but not in today's world. With the 10,000 watt radars, the minimum safe distance is 11.5' for human tissue, and with the 20-24 watt radars you can put your belly to the radome and read a book. Injury is caused by focus(antenna), frequency (penetration), power (heat) and time, how long you want to bar-b-que someone.

However, if you believe it prevents bird strikes, turn it ON. 1. You'll be distracted if you're not doing something you believe is valid or may be, and 2. The magnetrons rarely get used enough anyway if it's a magnetron unit.

2. You dont' have a phased array antenna, you have a flat plate. The phased array scans across the stationary antenna 'electrically'. Fighters need the phased array. Imagine a sweep and enemy at 1 o'clock and locked on, now unable to see the one at 10 o'clock.

3. Without a doubt you have a 30" antenna and 3 degree beam, understanding that the beam width is from the beam center to the 'half-power points', not a precise beam.

If you had a dual sweep system, the left sweep would belong the Capt and whatever the left control panel has selected and then obey the right control panel sweeping to the right. Since you state that you have units with color on one side and monochromatic on the other, that doesn't sound modern enough to enjoy independent settings (but, it's possible. The display is exactly that....a display...and nothing more). In those units with dual sweep, it obeys the tilt and range setting of each control panel independently, including in the low powered radars, the changing of the pulse width (same as length) that's transmitted and the PRF (Pulse Repetition Frequency) for that range. Low powered radars can transmit a pulse of 3.5 microseconds in close (3,500' in length) to 28.5 (28,500') in the 300 mile range. Nothing changes the shape of the beam.

StratoStallion
www.davegwinn.com

PS: Sometimes I type something so incredibly brilliant that I have to pause and think:
"Damn, I didn't know that!"