Airliner destroyed landing short after holding for a Cb. 100 survivors.
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Airliner destroyed landing short after holding for a Cb. 100 survivors.
It has happened before & we are unfortunately overdue for another windshear / microburst accident.
During 12 years of contract flying with medium size airlines, some of them national carriers, indications are that there is very little or no understanding of microbursts. Many of my first officers are now captains. I did my best to prepare them for their first serious encounter, but the painful lack of understanding has not made a quantum leap with the addition of their 4th bar.
In addition to poor knowledge and understanding, some airlines are insisting that a stabilized approach includes very low altitude profile corrections to achieve 1500 ft touchdown. The pressure really is on the expat pilot to conform. In some cases correct procedure will cause reversion to job hunting mode. Which airline is this?
Insurance is no substitute for safe operation. I am so surprised that the insurance companies are not professionally assessing such matters in individual airlines to modify premiums.
During 12 years of contract flying with medium size airlines, some of them national carriers, indications are that there is very little or no understanding of microbursts. Many of my first officers are now captains. I did my best to prepare them for their first serious encounter, but the painful lack of understanding has not made a quantum leap with the addition of their 4th bar.
In addition to poor knowledge and understanding, some airlines are insisting that a stabilized approach includes very low altitude profile corrections to achieve 1500 ft touchdown. The pressure really is on the expat pilot to conform. In some cases correct procedure will cause reversion to job hunting mode. Which airline is this?
Insurance is no substitute for safe operation. I am so surprised that the insurance companies are not professionally assessing such matters in individual airlines to modify premiums.
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My recollection of the last accident attributed to a microburst was July 2, 1994 (USAir 1016). Do you know of a more recent one??
We are definitely coming up to the mb season; June, July, August.
EAL 66 - June 24, 1975
Alegheny 121 - June 23 1976
PAA 756 - July 9, 1982
DAL 191 - August 2, 1985
USAir 1016 - July 2, 1994
That's just in the US, and those are only the biggies, there are more lesser known accidents/ incidents.
For a microburst refresher try:
http://www-frd.fsl.noaa.gov/mab/microburst/
We are definitely coming up to the mb season; June, July, August.
EAL 66 - June 24, 1975
Alegheny 121 - June 23 1976
PAA 756 - July 9, 1982
DAL 191 - August 2, 1985
USAir 1016 - July 2, 1994
That's just in the US, and those are only the biggies, there are more lesser known accidents/ incidents.
For a microburst refresher try:
http://www-frd.fsl.noaa.gov/mab/microburst/
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Which airline is this you ask? Youll have to tell us which area the airline comes from. I could make a pretty good couple of guesses though.
Ive had 2 microbursts (737) in the tropics which is exremley rare I must say.
* R24 MNL during the onset of the crossing of a typhoon edge moving E-W: 65 kts at 2000ft on final decreasing to 40kts by 1000ft. Tower wind was 25 kts gusting 35 with 5000M moderate rain. Very heavey dark rain observed on short finals.
At 400 ft at Vref+10 just becoming visual the nose dived and the wind went from 5kt tailwind componant to sudden 43 kt tailwind! Go around to stick-shaker with fire-walled throttles flown and recovered at 50ft, 3/4 way down the runway. Reported the incident and diverted. No prev reports from FEDEX aircraft who landed 12 minutes ahead.
* (actual microburst?) R20L SIN in heavey TS: At 2500 ft encountered extreme downdraft just before G/S intercept which required full throttle to maintain a 1200-1500 ft ROD at Vref-15 knots with intertmittant stick-shaker. Level flight gradient -capable after 15-20 loooong secs. Was suddenley GA gradient-capable after another 5 secs at 350ft, about 4nm from the runway. Reported the incident and got the hell out. No other prev reports but the cells were rapidly moving E-W.
Pants-crappin stuff indeed since they both occured at night! Had I not used the correct technique I think it couldve been far worse. Pretty rare in the tropics as I said where your worst problems tend to be approach downdraughts, and cross-wind and visibility nearing the ground. Anyone else know of MBs within tropic lattitudes?
Ive had 2 microbursts (737) in the tropics which is exremley rare I must say.
* R24 MNL during the onset of the crossing of a typhoon edge moving E-W: 65 kts at 2000ft on final decreasing to 40kts by 1000ft. Tower wind was 25 kts gusting 35 with 5000M moderate rain. Very heavey dark rain observed on short finals.
At 400 ft at Vref+10 just becoming visual the nose dived and the wind went from 5kt tailwind componant to sudden 43 kt tailwind! Go around to stick-shaker with fire-walled throttles flown and recovered at 50ft, 3/4 way down the runway. Reported the incident and diverted. No prev reports from FEDEX aircraft who landed 12 minutes ahead.
* (actual microburst?) R20L SIN in heavey TS: At 2500 ft encountered extreme downdraft just before G/S intercept which required full throttle to maintain a 1200-1500 ft ROD at Vref-15 knots with intertmittant stick-shaker. Level flight gradient -capable after 15-20 loooong secs. Was suddenley GA gradient-capable after another 5 secs at 350ft, about 4nm from the runway. Reported the incident and got the hell out. No other prev reports but the cells were rapidly moving E-W.
Pants-crappin stuff indeed since they both occured at night! Had I not used the correct technique I think it couldve been far worse. Pretty rare in the tropics as I said where your worst problems tend to be approach downdraughts, and cross-wind and visibility nearing the ground. Anyone else know of MBs within tropic lattitudes?
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Great accounts, I was on the edge of my chair, had I some popcorn it would've been like the cinema.
Microbursts in the tropics do appear less common, it has been postulated that the melting of hail, especially in the last 1,000 meters, is required to initialize the downdraft in a wet microburst. Negative buoyancy (dry/ cold air) is responsible for dry microburst formation, this lack of cold dry air and hail melting/ subliming well above 1,000 meters may account for a reduction in probability in the tropics. Haven't found any new data, but some incidents/ accidents from the tropics include: Pago Pago, Mexico City, Kano, Bombay, Doha, Bahrain, Naha, and not a small one in Chihuahua.
Microbursts in the tropics do appear less common, it has been postulated that the melting of hail, especially in the last 1,000 meters, is required to initialize the downdraft in a wet microburst. Negative buoyancy (dry/ cold air) is responsible for dry microburst formation, this lack of cold dry air and hail melting/ subliming well above 1,000 meters may account for a reduction in probability in the tropics. Haven't found any new data, but some incidents/ accidents from the tropics include: Pago Pago, Mexico City, Kano, Bombay, Doha, Bahrain, Naha, and not a small one in Chihuahua.
Last edited by '%MAC'; 6th May 2002 at 03:32.
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MAC Ive no doubt the MNL encounter was a microburst and the SIN event was very microburst-like. Of course I didnt notice the TAT at the time but it wouldve been interesting to see what numbers were there.
In both cases it wasnt like a sudden rapid increase in sink rate and loss of airspeed but more a sudden feeling of the aircraft rapidly trying to depart from under your bum. It was like your seat suddenley falling away from under you and your arse needing time to catch up. This feeling registered just at the onset of airspeed decay followed by GPWS "windshear!" activation. And believe me the sudden nose-down tendencey of an aircraft that was previously in-trim 30-40kts faster is bloodey terrifying.
Must admit both encounters rattled me a bit (screaming GPWS "windshear!" "sink rate!" "glide-slope! whoop whoop pull up!" didnt help at the time!) and took a while before I was "brave" enough to make approaches in realy crappey tropical wx again.
PS Oh and sorry it was 550ft recovery-height in SIN not 350ft as previousley stated.
In both cases it wasnt like a sudden rapid increase in sink rate and loss of airspeed but more a sudden feeling of the aircraft rapidly trying to depart from under your bum. It was like your seat suddenley falling away from under you and your arse needing time to catch up. This feeling registered just at the onset of airspeed decay followed by GPWS "windshear!" activation. And believe me the sudden nose-down tendencey of an aircraft that was previously in-trim 30-40kts faster is bloodey terrifying.
Must admit both encounters rattled me a bit (screaming GPWS "windshear!" "sink rate!" "glide-slope! whoop whoop pull up!" didnt help at the time!) and took a while before I was "brave" enough to make approaches in realy crappey tropical wx again.
PS Oh and sorry it was 550ft recovery-height in SIN not 350ft as previousley stated.
And as for our Aircraft Operating Manual (here), which specifies, nowadays, a maximum approach speed of Vref+5 knots: what a joke, if wind gusts are strong, or turbulence is moderate... and your plane is relatively light and the runway is long and dry, why not add about 5-10 more knots? Nobody can keep the speed within even a few knots of the desired "target speed' in gusty conditions anyway, neither can autothrottles (on a 757). When tower reports that a 737 gained 15 knots at 500 feet, who can guarantee that this can not change quickly to a serious airspeed loss?
I often wonder if the speed limitations to a long concrete (with no tail wind) runway are dictated by our program managers for 1) cross-fleet standardization, 2) to please the FAA's legal requirements (that's all they care about), or because 3) these guys only fly in good weather.
Does anyone else at a US airline have any ideas?
I'm dreading the summer and our pizza-oven cockpits already: the twin-turbofan type from the mid-60s, with turqouise decor. "Just a cup of ice please, styrofoam makes no difference".
I often wonder if the speed limitations to a long concrete (with no tail wind) runway are dictated by our program managers for 1) cross-fleet standardization, 2) to please the FAA's legal requirements (that's all they care about), or because 3) these guys only fly in good weather.
Does anyone else at a US airline have any ideas?
I'm dreading the summer and our pizza-oven cockpits already: the twin-turbofan type from the mid-60s, with turqouise decor. "Just a cup of ice please, styrofoam makes no difference".
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Ignition Override,
I assume you’re adding ½ the steady wind and all the gust, not to exceed 20kts on to Vref, per the Douglas manual? I’m sure your airline runs a safe operation, it would be unconscionable to think otherwise.
When overruns start becoming prevalent in the industry (AAL 1420) there is a call for reduced approach speeds, and when accidents happen that are attributed to microburst events then there is resumed talk of increasing speeds. There has to be a happy medium and you really already addressed this in your post about the dry runways. To answer your rhetorical question, just because I’m line and not management, I’ll answer 3.
Safe flying in your turquoise pizza heater.
Along with the loss of lift created by shifting winds in a microburst, wave type winds excite the phugoid frequency of transport category airplanes, additionally degrading performance. The phugoid, a resonant frequency of the airplane, is a low frequency longitudinal instability. The phugoid instability will cause oscillations in the aircraft’s airspeed and height, which may result in the airplane stalling, or impacting the terrain at a higher airspeed then stall.
Examples include:
ALG 121: A DC-9-30 crashed in a 10 degree nup attitude with engines producing 1.86 epr, flap at 15, gear retracted. Go around initiated at about 160 kias and low altitude, between 200 ft and 100 ft agl. Impact at 156 kts. They gained around 300 feet of altitude and their slowest speed was 120 kias.
DAL 191: An L-1011-385-1 was at 175 kts 2 secs prior to impact, 167 kts 1 sec prior and first hit was at 169 kts (corrected airspeeds).
USAir 1016: A DC-9-31 also hit at relatively high airspeed, about 150 kias.
PAA 806: A B-707-321B went in at 140 kias
EAL 66: A B-727-225 was at 150kias, then dropped to 140kias and in at 135ish, within 20 seconds.
In landing configuration, or go-around for ALG 121 and USAir 1016, these speeds are not extraordinarily slow. A NASA research paper (TN D-8496) states it this way: “it was found that positive wind shear can cause the phugoid to become aperiodic and unstable.”
Oh yea, more reasons to avoid microbursts.
I assume you’re adding ½ the steady wind and all the gust, not to exceed 20kts on to Vref, per the Douglas manual? I’m sure your airline runs a safe operation, it would be unconscionable to think otherwise.
When overruns start becoming prevalent in the industry (AAL 1420) there is a call for reduced approach speeds, and when accidents happen that are attributed to microburst events then there is resumed talk of increasing speeds. There has to be a happy medium and you really already addressed this in your post about the dry runways. To answer your rhetorical question, just because I’m line and not management, I’ll answer 3.
Safe flying in your turquoise pizza heater.
Along with the loss of lift created by shifting winds in a microburst, wave type winds excite the phugoid frequency of transport category airplanes, additionally degrading performance. The phugoid, a resonant frequency of the airplane, is a low frequency longitudinal instability. The phugoid instability will cause oscillations in the aircraft’s airspeed and height, which may result in the airplane stalling, or impacting the terrain at a higher airspeed then stall.
Examples include:
ALG 121: A DC-9-30 crashed in a 10 degree nup attitude with engines producing 1.86 epr, flap at 15, gear retracted. Go around initiated at about 160 kias and low altitude, between 200 ft and 100 ft agl. Impact at 156 kts. They gained around 300 feet of altitude and their slowest speed was 120 kias.
DAL 191: An L-1011-385-1 was at 175 kts 2 secs prior to impact, 167 kts 1 sec prior and first hit was at 169 kts (corrected airspeeds).
USAir 1016: A DC-9-31 also hit at relatively high airspeed, about 150 kias.
PAA 806: A B-707-321B went in at 140 kias
EAL 66: A B-727-225 was at 150kias, then dropped to 140kias and in at 135ish, within 20 seconds.
In landing configuration, or go-around for ALG 121 and USAir 1016, these speeds are not extraordinarily slow. A NASA research paper (TN D-8496) states it this way: “it was found that positive wind shear can cause the phugoid to become aperiodic and unstable.”
Oh yea, more reasons to avoid microbursts.
Can't say I've had the pleasure yet of a full blown actual MB. But have flown where you have 65 kts at 1000' down to 15 kts on the deck. Company uses Reference Ground Speed technique and I don't understand why it hasn't really taken on with many other carriers.
For those not familiar, RGS is a method of trying to maintain not only your aircraft IAS but also a minimum energy = at no stage through the final approach should you get bellow the ground speed (energy state) at which you expect to land.
For instance; Vref 154 kts at airport XYZ elevation 2000'
ATIS; Rwy 36 (360 deg) wind 060/30, CAVOK, temp 20 deg QNH 1013 reported 1000' wind 360/45.
So your RGS would be 154 kts
+ 4 kts for elevation (1 kts per 500')
+ 2 kts for temp (ISA @ 2000' = 11 deg, 20deg = +9, add 1 kts per 5 degs)
- 15 kts for expected headwind component on the runway.
= RGS 145kts
At least on the early part of the approach, down to say 1000', you would not allow your ground speed to drop below this figure. From around a 1000' and 500' (our minimum "stable" altitude) you should have final flap out and also respect a maximum of Vref + 25 kts whilst trying to maintain the RGS. All things being equal, by the time you get to the fence you should be roughly on speed at Vapp, having used the RGS technique, no large thrust increases should have been needed through the approach to drag up a decaying airspeed.
Unfortunatly this doesn't help much with a significant tailwind at 1000' or so as you must naturally still respect Vapp as minimum. In general though, use of the groundspeed during approach gives you a good indication of the energy in the airframe. I hope you could follow this - it's too early here to explain any better.
For those not familiar, RGS is a method of trying to maintain not only your aircraft IAS but also a minimum energy = at no stage through the final approach should you get bellow the ground speed (energy state) at which you expect to land.
For instance; Vref 154 kts at airport XYZ elevation 2000'
ATIS; Rwy 36 (360 deg) wind 060/30, CAVOK, temp 20 deg QNH 1013 reported 1000' wind 360/45.
So your RGS would be 154 kts
+ 4 kts for elevation (1 kts per 500')
+ 2 kts for temp (ISA @ 2000' = 11 deg, 20deg = +9, add 1 kts per 5 degs)
- 15 kts for expected headwind component on the runway.
= RGS 145kts
At least on the early part of the approach, down to say 1000', you would not allow your ground speed to drop below this figure. From around a 1000' and 500' (our minimum "stable" altitude) you should have final flap out and also respect a maximum of Vref + 25 kts whilst trying to maintain the RGS. All things being equal, by the time you get to the fence you should be roughly on speed at Vapp, having used the RGS technique, no large thrust increases should have been needed through the approach to drag up a decaying airspeed.
Unfortunatly this doesn't help much with a significant tailwind at 1000' or so as you must naturally still respect Vapp as minimum. In general though, use of the groundspeed during approach gives you a good indication of the energy in the airframe. I hope you could follow this - it's too early here to explain any better.
The waves of silence are crashing over!
Does anyone else use RGS? I believe it's a great tool assisting in windshear type environments. If your not using it, why not? Happy to hear any good arguments.
Does anyone else use RGS? I believe it's a great tool assisting in windshear type environments. If your not using it, why not? Happy to hear any good arguments.
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Muddy theres nothin wrong with that but its a bit complicated mate when Nature is throwing huge buckets of water in your face with sudden 30 kt windshifts and lightning, and your flat out just keeping the sky and runway where they should be!
Why not just simpley hold GS while keeping an eye on IAS and be done with it? I do.
Given: (737)
Vref = 133 kts (flap 40)
rwy 36
wind 350-030/30G45
1200m TSRA
So Steady wind = 15kt additive
mean Gust = 15kt
total IAS additives = +30 kts
:. approach IAS = 163 kts (vref + 33kts)
(*737-300 max additive = +20kts and also 163kts is over the structural speed for for flap 40. :. fly flap 30 which has higher limit).
So to protect your much-desired additives (especialy in conditions like these):
* take a flap 30 vref instead (138 kts).
* mean GS expected = 123 kt @ 138 kt IAS + your gust of 15kts = 138kt
So (assuming wind stays as advertised) hold GS at 138kt reducing to 123 kt over the fence irrespective of the higher IAS (remember runway landing distances actualy used are dictated by GS on touchdown, not IAS).
* As mentioned some aircraft may require reduced flap setting if IAS additives are too structuraly high for the higher landing flap.
PS main danger is attempting a smooth touchdown which could result in a prolonged float especialy at lower flap settings and higher than normal IAS's.
Why not just simpley hold GS while keeping an eye on IAS and be done with it? I do.
Given: (737)
Vref = 133 kts (flap 40)
rwy 36
wind 350-030/30G45
1200m TSRA
So Steady wind = 15kt additive
mean Gust = 15kt
total IAS additives = +30 kts
:. approach IAS = 163 kts (vref + 33kts)
(*737-300 max additive = +20kts and also 163kts is over the structural speed for for flap 40. :. fly flap 30 which has higher limit).
So to protect your much-desired additives (especialy in conditions like these):
* take a flap 30 vref instead (138 kts).
* mean GS expected = 123 kt @ 138 kt IAS + your gust of 15kts = 138kt
So (assuming wind stays as advertised) hold GS at 138kt reducing to 123 kt over the fence irrespective of the higher IAS (remember runway landing distances actualy used are dictated by GS on touchdown, not IAS).
* As mentioned some aircraft may require reduced flap setting if IAS additives are too structuraly high for the higher landing flap.
PS main danger is attempting a smooth touchdown which could result in a prolonged float especialy at lower flap settings and higher than normal IAS's.
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Hey Muddy,
Enjoyed your post about RGS, I don’t fly anything with INS so I have never used the technique as you described. I think Flying Tiger used IRGS, maybe it crept into Fed Up. Both the FAA and Boeing advise against using this technique for microbursts. (I am not saying that they know best – because I don’t think they do.) But if it is contrary to their recommendations, few if any airline will adopt the policy of IRGS.
Quote from AC 00-54
Slasher,
Don’t know that the TAT would have told you anything. I read your post about CAT and that you get a temp drop several seconds prior to encounter. I don’t know (and I don’t think anybody does) if you get a similar phenomenon with microbursts. I am looking at data from 186 microbursts documented in the JAWS (Joint Airport Weather Studies) project. The core temps in this data run the range of positive and negative delta Ts. Fujita, the expert, found no correlations in the data. There is a researcher (Wakimoto) that suggests that wet microbursts are warmer then the ambient atmosphere. Don’t know how he reaches that conclusion. (Still trying to access his work.)
The accounts of your experiences both point toward microbursts. Have to say you win the rather you than me award. Any cumulus cloud can spawn a microburst. Innocuous clouds can produce them when one isn’t expecting it, and they need not be turbulent. The pilots of USAir 1016 were not aware they were in a microburst because it wasn’t turbulent like all the microbursts they experienced in the sim. And the flight attendant that survived the Eastern 66 crash commented that the approach was not bumpy.
As for how to escape microbursts, that’s up to you guys. The escape maneuver in use today, pitch for 15 degrees or stick shaker... you know the one, was developed in a Boeing 727 simulator for 727s. In their research Boeing states that ‘we are aware other procedures may provide greater performance, yadda yadda...’ That’s a paraphrase, cause I can’t find the quote right now. They do say the procedure was chosen because it’s easy to remember and do. Several researchers are doing variable pitch guidance strategies which give better escape potentials. Journal of Aircraft had one such article titled “Escaping Microburst with Turbulence: Altitude, Dive, and Pitch Guidance Strategies” (May-June 2000).
Happy Flying
Enjoyed your post about RGS, I don’t fly anything with INS so I have never used the technique as you described. I think Flying Tiger used IRGS, maybe it crept into Fed Up. Both the FAA and Boeing advise against using this technique for microbursts. (I am not saying that they know best – because I don’t think they do.) But if it is contrary to their recommendations, few if any airline will adopt the policy of IRGS.
Quote from AC 00-54
Use of inertial reference ground speed emphasizes control of speed which is contrary to the recommended recovery technique. In addition, this technique is oriented toward compensating for the windshear and continuing the approach rather than immediately initiating the recovery maneuver. While this technique is not appropriate for microburst encounters, it may be suitable for use in other types of windshears.
Slasher,
Don’t know that the TAT would have told you anything. I read your post about CAT and that you get a temp drop several seconds prior to encounter. I don’t know (and I don’t think anybody does) if you get a similar phenomenon with microbursts. I am looking at data from 186 microbursts documented in the JAWS (Joint Airport Weather Studies) project. The core temps in this data run the range of positive and negative delta Ts. Fujita, the expert, found no correlations in the data. There is a researcher (Wakimoto) that suggests that wet microbursts are warmer then the ambient atmosphere. Don’t know how he reaches that conclusion. (Still trying to access his work.)
The accounts of your experiences both point toward microbursts. Have to say you win the rather you than me award. Any cumulus cloud can spawn a microburst. Innocuous clouds can produce them when one isn’t expecting it, and they need not be turbulent. The pilots of USAir 1016 were not aware they were in a microburst because it wasn’t turbulent like all the microbursts they experienced in the sim. And the flight attendant that survived the Eastern 66 crash commented that the approach was not bumpy.
As for how to escape microbursts, that’s up to you guys. The escape maneuver in use today, pitch for 15 degrees or stick shaker... you know the one, was developed in a Boeing 727 simulator for 727s. In their research Boeing states that ‘we are aware other procedures may provide greater performance, yadda yadda...’ That’s a paraphrase, cause I can’t find the quote right now. They do say the procedure was chosen because it’s easy to remember and do. Several researchers are doing variable pitch guidance strategies which give better escape potentials. Journal of Aircraft had one such article titled “Escaping Microburst with Turbulence: Altitude, Dive, and Pitch Guidance Strategies” (May-June 2000).
Happy Flying
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Pizza Oven
Ignition Override--At our "silver" airline, using "red and white" proceedures(still) we just add the full gust factor. Anyone who uses auto-throttles on any approach other than Cat II/III either has no confidence in their abilities or hasn't been bitten yet!
I just switched from the 717 to the -80 and didn't trust either system in any kind of windy conditions. Just my opinion, though.
Some guys flew the A/T's on the 717 all the way to landing even on good days. Oh, well...TC
P.S.--How hot are the "turquoise ovens" gonna get this summer with that door closed all the time?
I just switched from the 717 to the -80 and didn't trust either system in any kind of windy conditions. Just my opinion, though.
Some guys flew the A/T's on the 717 all the way to landing even on good days. Oh, well...TC
P.S.--How hot are the "turquoise ovens" gonna get this summer with that door closed all the time?
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Thanks folks, for the replies with valuable input. Its really sad that just about everyone I have flown with has no significant knowledge of thi subject. I am sure they all answered the appropriate met questions for ATPL etc, but the real nitty gritty is missing.
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Wow, from where did you resurrect this thread?
The nitty-gritty is absolutely missing, not only from an aviation perspective, but also from the vantage point of atmospheric physics. Several large research projects have been undertaken by various interested institutions, and a large amount of data has been collected. However the conclusions appear rather equivocal.
There are some indications when the atmosphere may be susceptible to microburst formation, but the ability to forecast location and timing has not yet been achieved. In geographical areas prone to dry type microbursts a dry adiabatic layer at altitude, or a rising inversion layer, seems to correlate to a probability of microburst formation. In tropical areas, a conducive environment for wet microbursts, the factors that influence their formation are height of the melting layer, lapse rate, mixing ratio in lowest 1000 meters, and mixing ratio at the melting level. One of the most important factors to emerge from the research is the lack of correlation between storm size and microburst intensity.
Most microburst induced accidents have occurred from flying under or through innocuous appearing CU. These storms were in a building stage and some became very large, however when the accident aircraft penetrated their boundaries they appeared quite benign. Large and threatening storms do not hold the same statistical significance probably because we avoid them more so then the average towering CU. From the post above, listing microburst induced accidents, all were a result of innocuous appearing clouds.
The physical mechanics of the microburst have been well documented with the help of FDR’s, TDWR, rawinsondes, and flight instrumentation (NASA actually flew their B737 through several). Vertical winds in excess of 26 meters/ sec (51 kts) and horizontal shears of 60 – 70 kts are probably fairly common for a good-sized microburst.
How and why microbursts form remains a mystery and contributes to the nitty-gritty lack of knowledge that is prevalent in aviation operations, meteorology, and even in the more academic arena of atmospheric physics.
There are some indications when the atmosphere may be susceptible to microburst formation, but the ability to forecast location and timing has not yet been achieved. In geographical areas prone to dry type microbursts a dry adiabatic layer at altitude, or a rising inversion layer, seems to correlate to a probability of microburst formation. In tropical areas, a conducive environment for wet microbursts, the factors that influence their formation are height of the melting layer, lapse rate, mixing ratio in lowest 1000 meters, and mixing ratio at the melting level. One of the most important factors to emerge from the research is the lack of correlation between storm size and microburst intensity.
Most microburst induced accidents have occurred from flying under or through innocuous appearing CU. These storms were in a building stage and some became very large, however when the accident aircraft penetrated their boundaries they appeared quite benign. Large and threatening storms do not hold the same statistical significance probably because we avoid them more so then the average towering CU. From the post above, listing microburst induced accidents, all were a result of innocuous appearing clouds.
The physical mechanics of the microburst have been well documented with the help of FDR’s, TDWR, rawinsondes, and flight instrumentation (NASA actually flew their B737 through several). Vertical winds in excess of 26 meters/ sec (51 kts) and horizontal shears of 60 – 70 kts are probably fairly common for a good-sized microburst.
How and why microbursts form remains a mystery and contributes to the nitty-gritty lack of knowledge that is prevalent in aviation operations, meteorology, and even in the more academic arena of atmospheric physics.
All,
The Reference Ground Speed approach method did originate with one thinking Captain in the old Flying Tigers, was picked up by a like minded Training Captain in Qantas, and it became “policy” in both airlines. It took them both years to break through the "conventional wisdom".
It is simplicity in itself, in planning an approach, and being aware of potential windshears, before you get there. You do need some form of ground speed readout, you don’t need IRS.
A RGS approach is actually a constant energy approach, if you think about it. Some of the formula mentioned made it look complicated, it is not, and it is only a trend indication.
All you are doing is figuring out, roughly, what your GS will be over the fence, based on reported wind and your TAS ( but at SL, unless it is stinking hot, the difference between IAS and TAS is not worth worrying about) Then, with a headwind, just fly the GS, with weather eye on the IAS. If the wind gradient from where you are to the lesser on the ground is uniform, the result will be almost constant power, as the IAS drops of, with the changing wind component ( no , I haven’t got it wrong) so the as you approach the threshold the IAS will have reduced to Vref+5 or whatever you use. Down the glideslope you will have gradually increased the nose attitude to maintain the approach slope, as the IAS decreases.
The value with microbursts is that you become very ground speed conscious, and generally you have to fly into a microburst to fly out ( Delta 1011 at ?? Dallas) and if you have a sudden increase in GS with cells around, you are headed into one, get the hell out.
If you only get hit with the increasing tailwind, with the RGS you might at least start off with a bit higher IAS than the usual from the traditional Boeing/Douglas half the steady wind plus the gust to max 20Kt additive. And thus a better chance of recovery.
Any of you who have flown the EA Kennedy wind shear profile in a sim. will remember that it was quite subtle, but still deadly.
Believe me, the RGS ground speed awareness is a life saver.
Tootle pip!!
The Reference Ground Speed approach method did originate with one thinking Captain in the old Flying Tigers, was picked up by a like minded Training Captain in Qantas, and it became “policy” in both airlines. It took them both years to break through the "conventional wisdom".
It is simplicity in itself, in planning an approach, and being aware of potential windshears, before you get there. You do need some form of ground speed readout, you don’t need IRS.
A RGS approach is actually a constant energy approach, if you think about it. Some of the formula mentioned made it look complicated, it is not, and it is only a trend indication.
All you are doing is figuring out, roughly, what your GS will be over the fence, based on reported wind and your TAS ( but at SL, unless it is stinking hot, the difference between IAS and TAS is not worth worrying about) Then, with a headwind, just fly the GS, with weather eye on the IAS. If the wind gradient from where you are to the lesser on the ground is uniform, the result will be almost constant power, as the IAS drops of, with the changing wind component ( no , I haven’t got it wrong) so the as you approach the threshold the IAS will have reduced to Vref+5 or whatever you use. Down the glideslope you will have gradually increased the nose attitude to maintain the approach slope, as the IAS decreases.
The value with microbursts is that you become very ground speed conscious, and generally you have to fly into a microburst to fly out ( Delta 1011 at ?? Dallas) and if you have a sudden increase in GS with cells around, you are headed into one, get the hell out.
If you only get hit with the increasing tailwind, with the RGS you might at least start off with a bit higher IAS than the usual from the traditional Boeing/Douglas half the steady wind plus the gust to max 20Kt additive. And thus a better chance of recovery.
Any of you who have flown the EA Kennedy wind shear profile in a sim. will remember that it was quite subtle, but still deadly.
Believe me, the RGS ground speed awareness is a life saver.
Tootle pip!!
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.All Airbus fly by wire a/c operate on a '.Ground Speed Mini' technique on approach. This is very similar to your RGS system except that the computers convert it into an equivalent indicated airspeed, so that the pilot can fly the aircraft normally.
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Re-inventing the wheel
In America we tend to suffer from a psychological maturity problem, the condition that if it isn’t invented here it is not worthwhile. This attitude permeates not only the Government, but individual companies, and dare say individuals. Numerous examples exist, from the war on terrorism, the war on drugs (lost), the inability to cope with runway incursions, and the national medical crises. Well, it’s not a rant but an observation and provides the underpinnings of why IRGS is not in common use.
The Eastern 66 crash was the catalyst for research into microbursts and precipitated many recommendations from the NTSB. One of the government-funded projects was FAA RD 66-166 in three phases. The company securing the contract was based in Southern California and used a DC-10 simulator, leased from Douglas, for their trials. Initially the RGS or IRGS system was evaluated and promising results were obtained. Several other microburst type accidents transpired, most notably Allegheny 121, and the NTSB requested new studies concerning guidance for flight through microbursts. Four companies bid on this lucrative grant, all of whom had projects in the initial stages of development. Boeing was using their 727 engineering simulator to test guidance strategies and was committed to a constant pitch maneuver. The contract was awarded to the Boeing Company... and that is pretty much the last we’ve heard about RGS. Boeing didn’t invent it and it appears they wanted nothing to do with it.
That it is discredited in AC 00- 54 yet showed promise in the research leads to some poignant questions. The IRGS approach has been dealt a premature death and really may provide a suitable means for mitigating the effects of microburst type winds. It would seem that, to a certain extent, Airbus takes this into consideration. Your individual airline may provide guidance in this area, or your country’s aviation authority. Don't look to the FAA or Boeing for guidance on this one.
Obviously the safest measure is avoidance.
The Eastern 66 crash was the catalyst for research into microbursts and precipitated many recommendations from the NTSB. One of the government-funded projects was FAA RD 66-166 in three phases. The company securing the contract was based in Southern California and used a DC-10 simulator, leased from Douglas, for their trials. Initially the RGS or IRGS system was evaluated and promising results were obtained. Several other microburst type accidents transpired, most notably Allegheny 121, and the NTSB requested new studies concerning guidance for flight through microbursts. Four companies bid on this lucrative grant, all of whom had projects in the initial stages of development. Boeing was using their 727 engineering simulator to test guidance strategies and was committed to a constant pitch maneuver. The contract was awarded to the Boeing Company... and that is pretty much the last we’ve heard about RGS. Boeing didn’t invent it and it appears they wanted nothing to do with it.
That it is discredited in AC 00- 54 yet showed promise in the research leads to some poignant questions. The IRGS approach has been dealt a premature death and really may provide a suitable means for mitigating the effects of microburst type winds. It would seem that, to a certain extent, Airbus takes this into consideration. Your individual airline may provide guidance in this area, or your country’s aviation authority. Don't look to the FAA or Boeing for guidance on this one.
Obviously the safest measure is avoidance.
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Micro Burst - Avoidance
The two microburst incidents I could have been involved in I avoided by requesting a hold on both occasions. They painted up very well on the WX radar & were clear in 15 minutes. Declining the approach in SIN did cause an ATC problem & I was vectored out of the area but then the following acft also declined the approach & was first acft in when the wx cleared.
%MAC put it in one word . Avoidance.
The WX Radar should not be on SBY in the terminal area until you are sure the final approach & missed approach paths are clear of weather.
%MAC put it in one word . Avoidance.
The WX Radar should not be on SBY in the terminal area until you are sure the final approach & missed approach paths are clear of weather.
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Autoflight, thank you for starting an interesting discussion.
Slasher very interesting accounts. Just for clarification in the first account you talk of an approach to MNL and the presence of moderate rain. Were there any heavy thunderstorms in the area at the time as well ? You only mention the presence of a nearby typhoon.
%MAC : The quote you give in your post showing how RGS approaches are not recommended by Boeing is for AC 00-54. Is there anywhere I can read the full article.
Mud Skipper : Just looking at some old manuals the Minimum Ground Speed approach was mentioned in the 747 Classic manuals. However it was aimed at occassions when strong winds persisted to low altitude and then disappeared before touchdown. There was also a note saying the method was not recommended for Microburst conditions, just like %MAC mentioned. Still I do agree that being aware of a minimum ground speed may be a good early warning sign that something nasty may be about to happen.
Capt. Crosswind :
"The two microburst incidents I could have been involved in I avoided by requesting a hold on both occasions. They painted up very well on the WX radar & were clear in 15 minutes. "
I presume there was other evidence, pilot reports, ATC reports, wind differentials between wind at altitude and on the ground, presence of virga, to lead you to believe a microburst was taking place. Unless your weather radar had predictive windshear then the microburst itself cannot be painted on the radar. What you are left with then is the presence of Thunderstorms on the approach which does not necessarily mean a microburst is taking place. To quote from the National Oceanic and Atmospheric Administration website
"Observations suggest that approximately five percent of all thunderstorms produce a microburst and significant wind damage can be related to them."
Reference : http://www.srh.noaa.gov/jax/events/windshear.html
By the way I'm not saying that if there are thunderstorms on the approach you should carry on for approach even though there are no reports of winshear or microburst. I like you would definitely assume the worst especially if I knew from local knowledge that they would clear in a matter of minutes.
While I agree strongly with the concept of avoidance (Who could possibly disagree) one should be aware that there are aspects of microbursts that may make them impossible to avoid. We have already talked about microbursts associated with innocuous CBs. Coupled with this in a very early study of microbursts in the US it was found that they usually have a life of about 3-4 minutes. Which means it is perfectly feasible that one aircraft could fly the approach with no adverse affects whild the following aircraft could encounter a severe microburst. Again something to be aware of.
Slasher very interesting accounts. Just for clarification in the first account you talk of an approach to MNL and the presence of moderate rain. Were there any heavy thunderstorms in the area at the time as well ? You only mention the presence of a nearby typhoon.
%MAC : The quote you give in your post showing how RGS approaches are not recommended by Boeing is for AC 00-54. Is there anywhere I can read the full article.
Mud Skipper : Just looking at some old manuals the Minimum Ground Speed approach was mentioned in the 747 Classic manuals. However it was aimed at occassions when strong winds persisted to low altitude and then disappeared before touchdown. There was also a note saying the method was not recommended for Microburst conditions, just like %MAC mentioned. Still I do agree that being aware of a minimum ground speed may be a good early warning sign that something nasty may be about to happen.
Capt. Crosswind :
"The two microburst incidents I could have been involved in I avoided by requesting a hold on both occasions. They painted up very well on the WX radar & were clear in 15 minutes. "
I presume there was other evidence, pilot reports, ATC reports, wind differentials between wind at altitude and on the ground, presence of virga, to lead you to believe a microburst was taking place. Unless your weather radar had predictive windshear then the microburst itself cannot be painted on the radar. What you are left with then is the presence of Thunderstorms on the approach which does not necessarily mean a microburst is taking place. To quote from the National Oceanic and Atmospheric Administration website
"Observations suggest that approximately five percent of all thunderstorms produce a microburst and significant wind damage can be related to them."
Reference : http://www.srh.noaa.gov/jax/events/windshear.html
By the way I'm not saying that if there are thunderstorms on the approach you should carry on for approach even though there are no reports of winshear or microburst. I like you would definitely assume the worst especially if I knew from local knowledge that they would clear in a matter of minutes.
While I agree strongly with the concept of avoidance (Who could possibly disagree) one should be aware that there are aspects of microbursts that may make them impossible to avoid. We have already talked about microbursts associated with innocuous CBs. Coupled with this in a very early study of microbursts in the US it was found that they usually have a life of about 3-4 minutes. Which means it is perfectly feasible that one aircraft could fly the approach with no adverse affects whild the following aircraft could encounter a severe microburst. Again something to be aware of.