{"id":87172,"date":"2025-02-14T06:35:03","date_gmt":"2025-02-14T06:35:03","guid":{"rendered":"https:\/\/peraltafinancing.com\/airline\/microburst-detection-and-avoidance-a-new-method-to-identify-the-threats\/"},"modified":"2025-02-14T06:35:03","modified_gmt":"2025-02-14T06:35:03","slug":"microburst-detection-and-avoidance-a-new-method-to-identify-the-threats","status":"publish","type":"post","link":"https:\/\/fivemor.com\/?p=87172","title":{"rendered":"Microburst detection and avoidance \u2013 A new method to identify the threats"},"content":{"rendered":"


\n<\/p>\n

\n

\"microburst<\/p>\n

\"microburst\"<\/p>\n

Microburst detection and avoidance<\/p>\n

A primer for pilots<\/p>\n

By Captain Shem Malmquist<\/p>\n

You\u2019re on final and there are thunderstorms around.\u00a0 As you line up still 10 miles out you notice that you can see the airport but there is some light rain in the vicinity of short final.\u00a0 Lightning is present in the area, but you are below the bases.\u00a0 Your radar is set to about 5 degrees nose up and not painting anything other than the light rain you see.\u00a0 There are no windshear warnings and you are equipped with predictive windshear.\u00a0 As you approach the FAF the aircraft in front of you, a CRJ 700, lands.\u00a0\u00a0 The tower asks them for a ride report and they report \u201csmooth all the way down\u201d.\u00a0 You can still see the airport through the continuing light rain.\u00a0 Are you safe to continue?<\/p>\n

The answer to this question depends.\u00a0\u00a0 I think we all know that most pilots would continue in this scenario.\u00a0 Is the airport equipped with a microburst detection system?\u00a0 \u201cA what?\u201d you ask.\u00a0 Is that not the same as a windshear detection system?\u00a0 Nope, we\u2019ll get to that shortly.<\/p>\n

Most all of the current guidance for microbursts follows along a series of things to look for and then recommendations should you encounter it.\u00a0 However, the items to look for are so common that they are often ignored, or, if followed, would preclude so many airline operations they would grind the system to a halt.<\/p>\n

Before I go further,\u00a0 I have a deep concern that we have convoluted \u201cwindshear\u201d and \u201cmicroburst\u201d.\u00a0 We can have a windshear from just the rolling effect that wind has over the surface.\u00a0 The surface friction leads to the air essentially rolling over on itself and causing gusts.\u00a0 We can also have a windshear in a similar manner with two different airmasses near each other.\u00a0 Adding a bit of speed is really all that\u2019s needed to handle this sort of \u201cshear\u201d.\u00a0 It is more of a \u201cgust additive\u201d, as that is the threat. That stated, the below is from the FAA Windshear Training Guide AC 00-54. It is important to remember that the HIGH items are mostly aspects that will occur once a microburst has \u201cdropped\u201d:<\/p>\n

\"windshear<\/p>\n

While the \u201chigh\u201d probability items are fairly straight forward, the \u201cmedium\u201d are not.\u00a0 Also, notice the caution?\u00a0 Clearly there are some gaps.\u00a0 With just minimal tools to avoid it in the first place, the industry turned to how to recognize you\u2019re in a microburst and how to best survive the event.\u00a0 These started with a description and image, likely similar to this one:<\/p>\n

That would be followed by something like this:<\/p>\n

\"windshear<\/p>\n

or maybe one like this:<\/p>\n

\"microburst\"<\/p>\n

The guidance for windshear recovery is well known and practiced in training often, but I will add it here as a good reminder, although the following is very generic (out of the FAA Windshear Training Guide) and so does not reflect methods that may be applicable to some current designs, it never hurts to review:<\/p>\n

\"windshear<\/p>\n

All that is great, but there are two parts to preventing a problem.\u00a0 Astronaut Frank Borman (Col,\u00a0USAF, Ret.) famously stated \u201cA superior pilot uses his superior judgment to avoid situations which require the use of his superior skill\u201d.\u00a0 For the most part, the guidance to on microbursts pilots falls into the \u201cskill\u201d part, and the avoidance of them is left to their intuition or just experience.\u00a0 Unfortunately, microbursts are rare enough that experience is likely not going to be enough.\u00a0 This may also be the reason we do not see more accidents.\u00a0 The odds of a microburst occurring very near the approach or departure path of an airport just when an airplane is there is, fortunately, quite low.<\/p>\n

Several years ago, while researching material for another project, I had some discussions with a few folks at MIT\u2019s Lincoln Laboratory.\u00a0 The Lincoln Lab had developed an algorithm to detect windshear that was not based on the \u201cafter the fact\u201d.\u00a0 To understand this, look back at the \u201ctypical descriptions\u201d we get of microbursts.\u00a0 The focus is all on the way a developed microburst manifests itself and what a pilot would experience flying through it.\u00a0 It starts with a building headwind, then a downdraft and finally a tailwind.\u00a0 The cues pilots are taught are built around that.\u00a0 Windshear alerting systems, both ground based and airborne are designed to look for the differences in the outward flow.\u00a0 They detect lateral flow, parallel to the ground, and if there is enough of a differential they signal a windshear.\u00a0 These systems work well for telling you that a microburst has <\/em>occurred, but what about detecting one that is about <\/em>to occur.\u00a0 The below image was developed on work initially done by Dr. Fujita (yes, the same Fujita that originated the scale for tornadoes). \u00a0This is showing where the water is in the storm, or \u201cVertically Integrated Liquid\u201d (VIL).<\/p>\n

\"fujita<\/p>\n

The following images come from several papers out of the Lincoln Lab.<\/p>\n

\"microburst<\/p>\n

What you can see is that, for simplicity, a microburst starts as a large updraft holding water aloft.\u00a0 That water finally gets so heavy that the updraft cannot hold it anymore, and so it starts to fall.\u00a0 It may fall directly down, or may be offset quite a bit depending on winds, etc.,\u00a0 As it falls it starts to evaporate, cooling it, and accelerating the flow.\u00a0 For practical purposes, the Lincoln Lab developed an algorithm that detects this mass of water aloft.\u00a0 The microburst detection systems they developed using this algorithm are now installed at approximately 67 U.S. airports and Hong Kong.\u00a0 They do not necessarily detect for every runway and the alert is not a \u201cwindshear alert\u201d from ATC but rather a \u201cmicroburst alert\u201d.<\/p>\n

Notice that in the earlier part of a microburst\u2019s life cycle the rain is all aloft.\u00a0 It will not<\/em> meet the \u201cHIGH criteria in that windshear guidance above! <\/strong>Now consider how your radar is set.\u00a0 If you are following what most pilots do, setting just a few degrees up to remove terrain, you are, literally, under-scanning <\/em>the threat!\u00a0 You will pick up next to nothing.\u00a0 Assuming that the Delta 191 crew was using \u201cstandard\u201d techniques, they would not have been painting much on their radar until it was too late.\u00a0 On final, you are below the rain, or maybe just a bit is starting to fall in a thin line that winds its way through the updrafts \u2013 sort of a path-finder for the larger mass.\u00a0 Your radar is picking up nothing of significance and you can visually see the runway.\u00a0 All looks great!\u00a0 It is literally \u201csuckering\u201d you in.\u00a0 Then you get too close to avoid it and the mass comes down.\u00a0 Look at the next couple of images.<\/p>\n

\"microburst<\/p>\n

\"microburst<\/p>\n

You do not want to be underneath one of these as it collapses on top of you!\u00a0 Going back to the vertical profile, below is an image a downburst (you can see my post here<\/a> for more background on it).\u00a0 Can you tell where you want to scan for the danger?<\/p>\n

\"NWS<\/p>\n

As you probably have surmised, the guidance in most radar manuals and instruction is generally telling us to scan too low to \u201csee\u201d the threat on approach and departure.\u00a0 The solution is to point your beam higher up.\u00a0 Pretty much all airborne radar that I am aware of have a maximum tilt of 15 degrees.\u00a0 Using the tilt formula, \u00a0one degree equals 1,000 feet at 10 miles, you can see that even at 15 degrees up the maximum you can \u201csee\u201d is 15,000 feet above the aircraft (a bit more depending on your beam width, most large aircraft have approximately 3.5 degrees wide beams).\u00a0 You can use the formula to see where to scan to capture the threat at<\/p>\n

The illustration below gives some insight.<\/p>\n

\"radar<\/p>\n

Have an automated system?\u00a0 Know how it works.\u00a0 Read the literature.\u00a0 Like any automated system, we must truly understand how it works to know how to get the information you need.\u00a0 It is very probable you\u2019ll have to \u201cwork around\u201d the auto mode to \u201csee higher\u201d.\u00a0 Some of these systems are further limited when they go into predictive windshear mode, limiting the vertical scan to increase the scan rate.\u00a0 Obviously, this creates a problem, but if you see more water aloft than down below, be careful.\u00a0 Pretty much the only way this can occur is hail, virga or an impending microburst.\u00a0 Of course, virga can be indication of a \u201cdry\u201d microburst as well.<\/p>\n

I have used this in the real world several times now.\u00a0 A couple of times I was showing my F\/O the technique before takeoff and pointing out how a storm looked like it met the profile for a microburst.\u00a0 On one occasion the storm was offset from the departure path so was not going to be a factor, but as we broke ground it \u201clet loose\u201d (several miles ahead and to our left) and we got a \u201cwindshear ahead\u201d alert as we could see the bottom fall out of the storm.\u00a0 On another we were in Denver and as we started to taxi I pointed out that as we rolled the tilt up to 15 it went from nothing to green, yellow and red.\u00a0 I said \u201cwe are going to have to take a look at this when we get aligned with the runway, but we may need to delay\u201d.\u00a0 Just 5 minutes later ATC called \u201cmicroburst alert\u201d and shut down the airport!<\/p>\n

Even if you can\u2019t get the beam high enough you might still be able to see high enough to get a slightly early warning of an \u201cimpending threat\u201d.\u00a0 Also, there really is no point in scanning the weather under 10,000 feet.\u00a0 You really can\u2019t tell whether what you\u2019re seeing is convective or just low altitude heavy rain without tilting upwards.<\/p>\n

One last caveat.\u00a0 Nothing is 100% sure.\u00a0 This method is just one more to put into your toolbox but continue to rely on all the cues you can get.<\/p>\n

\u00a0<\/p>\n