Gunnar Fahlgren

Risken för Tail Wind accidents minskar för Airbus.

Ursprungligen var det när hjulen började rulla (wheel spinn up) som spoiler skulle öppna sig. Problemet var, att vid hala banor blev det ingen rotation på hjulen och spoilers förblev infällda. Resultatet blev ett antal avåkninger från landningsbanan.

Efter många år av påpekanden om att det borde införas en möjlighet för piloten att öppna spoilers manuellt (som på alla andra flygplantyper) så har nu Airbus infört andra modifieringar, som förbättrar systemet.

1. Nu är det radarhöjdmätaren (6 fots höjd) som, i kombination med idle, utlöser spoiler. När de är armerade inför landning.

2. Vidare har man tagit bort kravet på att co-pilot ropar (a call out) ”spoiler out,” innan reversering får ske.

3. Och dessutom har man nu lagt in en extra signal till spoiler att öppna sig när reverseringen inleds.

4. Vid hård landning (on ground mode) öppnas spoilers även om throttles är över idle.

Allt detta gör att systemet nu har förbättrats, så att Airbus inte anser sig behöva införa manuell extension.

Vi får nöja oss med detta och hoppas att framtiden kan utvisa, att den manuella utlösningen inte ska behövas.

I just read “Slippery Surprise” in the latest copy of Flight Safety Foundation’s excellent magazine Aero Safety World, April 2010. (Google: asw apr 10 pdf)

An Airbus 321 left the runway at Sandefjord, Norway March 26,2006. It was tailwind, very slippery runway probably causing no wheel spin up and therefore probably no deployment of spoilers and no function of auto brakes. Maximum manual breaking and even parking brakes gave no effect. Wheels were gliding on top of slush. (No surprise for me)

If it had been possible to extend spoilers manually, the load on wheels had increased giving contact with the runway surface.

So this was a ”design induced accident/incident” in combination with tailwind.

Compare with the Airbus 340 at Toronto August 2,2005. It also had tailwind, no wheel spin up and consequently no deployment of spoilers. (Google: Flight 358)

Airbus is, so far as I know, the only aircraft type where spoilers can´t be extended manually.And that stupid construction causes many accidents and incidents killing people and destroying Airbuses. Good business for Airbus. They can sell more aircraft to replace the crashed ones.

http://flightsafety.org/asw/mar07/asw_mar07_p46-47.pdf

Date:22 MAY 2010 Time:ca 06:10 Type:Boeing 737-8HG(WL) Operator:Air India Express

Runway 24 has an available landing distance of 2450 m.

The visibility was approximately six kilometers, winds were calm, there was no rain and the runaway was dry."

On video recordings from the accident it is possible to see the smoke drifting from the tail and forward.

This indicates a slight tail wind during landing.

Definitely the pilot had problems to reduce speed but decided to land instead of making a go around.

A very common reason for high speed during approach is a considerable tail wind at higher altitude.

Compare with this accident at the same airport 29 years ago

Date:18 AUG 1981 Type:Hindustan Aeronautics Ltd. HAL-748-224 Srs. 2 Operator:Indian Airlines

The aircraft approached Mangalore and landed half way down the runway. The aircraft overran the runway and nosed over into a valley after the choice of landing on down-sloping runway with a tail-component."

From Google bout he northeasterly trade winds:

Northeast winds over the tropical Atlantic and The Pacific Ocean.

Wind direction and wind speed are virtually constant years

around. Conclusion: This trade wind gives tail wind when landing on R/W 24.

Date:12 MAY 2010 Time:06:10 Type:Airbus A330-202 Operator:Afriqiyah Airways

The airplane crashed and broke up about 900 m from the runway 09 threshold and 200 m to the south of the extended centreline.

HLLT 120420Z 27007KT 5000 BR NSC 19/17 Q1009= [04:20 UTC; Winds 270 degrees at 7 knots; visibility 5000m

Date:22 DEC 2009 Time:22:22 Type:Boeing 737-823 (WL) Operator:American Airlines

Landing on runway 12 during a rainstorm. The plane skidded across a road and came to rest on a beach.

Current information indicates that given the wind direction of 320 degrees at 8 knots, the airplane carried out a tailwind approach and landing on runway 12.

As an answer to comments I have got, regarding tail wind, I will clarify my point of view with this statement.

I never say that an accident is caused by tailwind.

I only say, that it happens in tail wind.

Statistically there seems to be a much higher risk for an accident to happen in tail wind compared to accidents in head wind. And what I try to do is to give an explanation to why tail wind is a contributing factor. 

An other comment:

Assume VREF=110 kts. With a 10 kt head wind at 15 ft in the touchdown zone, groundspeed is 100 kts. With 10 kt tail wind it is 120 kts. The energy of the airplane is 44% higher and substantially longer runway would be needed. But if calculations show that available field length is adequate, where is the problem?

And my aswer:

Your calculation is correct. The problem is that VREF and height over the runway end are not reached in an approach with tail wind in the approach area. The tail wind on ground is not so important. It is the wind during approach, which will cause problem.

If stabilized on glide path and speed the aircraft might be landed short when the tail wind suddenly is reduced close to ground or if not so, the aircraft might come in “hot and high” and make a long landing.

That tail wind effect in combination with a wet and/or slippery runway or no manual extension of spoilers will cause problems if the pilot dos´nt make a go around.

Gunnar

An other comment: "Sudden reduction" applies to wind shears, right? I'd use correct terminology, or readers can be misled.

My answer:

Maybe you are right, but for me a wind shear is a sudden change of wind direction. A sudden change of wind speed you always have in all approaches both in head wind and in tail wind, when the wind speed is reduced closer to ground due to orography

Gunnar

Quoted from Wikipedia

In aeronautics, a tailwind is unfavourable in takeoffs and landings. As a result, aviators and air traffic controllers commonly choose to takeoff or land in the direction of a runway that will provide a headwind.

Tailwind accidents Type One

This type of accident might happen to both professional pilots and less experienced pilots. 

Most of our approaches are made in headwind. The wind component is then normally a bit stronger at initial approach altitude, 1500/2500 feet, than on the runway.

A great majority of all approaches are made under such conditions. And the pilot, or his auto throttle,will gradually reduce power, hardly noticeable, when he is approaching ground and his headwind is reduced. 

What will happen inan IFR tailwind approach? 

Most airport procedures accept landings with a tailwind up to 10 knots. That authorization gives a false impression that a tailwind approach won't cause any problems.

But let us analyze the approach step by step. 

Let us say that you are going to make a landing on runway 01. The surface wind is 180 degrees at 3knots. A tailwind component of 3 knots should not pose a problem – or? 

But at 2000 feet above ground the wind might be 180 degrees, 24 knots. The main change of wind speed,due to the orography, will usually occur at around 400 - 600 feet elevation.

If the aircraft is stabilized on glide path in a fully automatic approach the following things can be noticed. 

1. Initially you will notice a much higher rate of descent than normal

2. When stabilized on speed, let us agree upon 140 knots, with full flaps and gear down, you have throttled back to a much lower power setting than normal. (Your 24 knots tailwind is acting as an extra engine pushing you forward). 

3.  When you approach 400 - 600 feet and the tailwind rapidly decreases, your airspeed indicator will – well what do you think?

Yes initially it will indicate a higher speed let us say 152knots. 

4. The response to this increased airspeed, from your skilled brain, or your auto throttle, will be a power reduction to get back the desired speed of 140 knots. 

5.  A few seconds later, with your aircraft still on glide path, your airspeed is rapidly dropping. It is falling not only to 140 knots but probably to 130 knots. The angle of attack is increasing. The drag is increasing enormously. 

6.  Now you have to increase power fast and distinctly and you might even end up with take off power to recover your desired speed of 140 knots and reach the runway.

7.  After landing you will most probablysay:

 – "Pugh, that was a hell of a windshear." 

Very few pilots will after landing scrutinize what actually happened. The fact is that you acted completely wrongly, when you reduced power when speed increased.

As your pushing wind –your "extra engine"– stops, you should INCREASE power instead to compensate for that power loss. Otherwise you will not reach the runway. 

Pilots have been taught to reduce power, when speed goes above a desired value. That has been trained and trained for years. It has been stored in your brain, in your Motor Memory,which will act automatically, like an auto throttle.

This wrong action has caused one or two heavy accidents - CFIT accidents - every year.

Most accidents when afully operative aircraft and crew hit the ground before, but rather close to,the runway, I would say, are caused by this tailwind effect. 

If I look at accidents,which have happened in Scandinavia or elsewhere with aircraft operated or owned by a Scandinavian airline, I can notice that about 80% of all accidents have occurred in tailwind. 

1. A domestic"Metropolitan" aircraft fatally crashed before the runway at Ängelholm Airport, Sweden 1964.

Tailwind 22 knots at 1000 feet. Night approach no glide path.

2. A DC-8 hit the water when approaching Los Angeles in January 1969. Tailwind changing to headwind. 

3. A Fokker F-28 crashedat Oslo Airport, Norway, in December 1972 during an approach in tailwind. 

4.  A tailwind approach to Madrid Airport  with a B-747, owned by SAS and leased by Avianca, ended up with a fatal crash in November 1983. 

5.  In 1986 a DC–9 had a severe incident, close to a crash, after a tailwind approach to Ålborg Airport, Denmark. 

6.  After having a tailwind component of 26knots at 1500 feet a DC-10 crashed at Kennedy Airport, USA in February1984. 

7.  In August 1989 a Beech 99 crashed before the runway at Oskarshamn Airport, Sweden. They had a tailwind changing to cross wind. 

Of course the tailwind is not the only reason for these accidents, but it is definitely a serious contributing factor.

As a countermeasure some new generation auto throttles have now been modified to increase power instead of making power reduction. They get information not only from air speed but also from ground speed.

As ground speed will decrease when tailwind is reduced, this auto throttle will compensate with more power and disregard the increase in air speed.

 This is exactly what human pilots should be trained for, namely to increase power when speed is increasing. 

Air speed makes your aircraft fly.

Ground speed brings your aircraft to the runway. 

 But what happens in a VMCapproach without an autopilot and without an ILS? 

 1.  You will notice a much higher rate of descent than normal.

2.  When stabilized on speed you have throttled back to a much lower power setting than normal.

3.  When you approach 400 - 600 feet andthe tailwind rapidly decreases, what will happen?    

Well, if you stick to your approach angle, air speed will temporarily increase. But most probably you will get high in the approach and maintain airspeed.

4.  The response to this increased elevation (or air speed) will be further power reduction and to start a dive to get back the desired speed and approach angle.

5.  A few seconds later, when your aircraft is back on desired approach angle, your airspeed is rapidly dropping. The angle of attack is increasing. The drag is increasing enormously.

6.  Now you have to firmly increase powerand you might even end up with take off power to recover your desired airspeed.

 The landing will in most cases be a very short landing. But if you are approaching the runway end, at full power and accelerating, you might also end up in the ditch at the end of avery short landing strip. 

 Things to be done to avoid this type of accident. 

1.  Avoid tailwind landings. Request another runway. 

2.  Do not accept an initial approachaltitude below 2500 feet. A longer approach will give you more time for preparation. 

3.  Be prepared to overpower your auto throttle. 

4.  Train your brain to respond with more power, when speed is increasing.  

5.  If you have to land in tailwind, ask the controller for actual wind at 2500 feet. Then you are prepared.

A good example, of what the effect of such a request might cause, is my approach to Copenhagen airport,Denmark.

I was cleared to land on runway 04 left. Actual wind was tailwind 6 knots. The following conversation took place.       

Tower from SK 401:

 – Request actual wind at 2500 feet.         

 – Stand by.  

 – Standing by. 

(Ten seconds later)      

–     SK 401, we are now changing to runway 22 left. Turn left to heading 020. Climb to 2500 feet and contact approach control.  

 In modern aircraft with GPS you can read the wind. If it indicates tailwind be prepared to increase power when speed is increasing.

 The problem is that tailwind landings will be more and more frequent, as it is a great problem for an airport controller to change to another runway with a lot of traffic in his control area.

If the wind is changing,the landings most probably will continue, as long as the limit of 10 knots tailwind is not exceeded, before a change will be done. 

At the time of the DC-10accident at Kennedy airport, mentioned above, I have been told that they deliberately used a tailwind runway, because they had used the opposite runway the day before. And the noise had to be evenly distributed due to a noise abatement request.

This I regard as a typical unprofessional decision. And we must never forget that noise abatement procedures are, and have always been, in conflict with flight safety.

Pilots who did not fly before 1959, when the first noise abatement procedures were implemented on the Caravelle, have never noticed the difference.  

Tailwind accidents type two

Sometimes the tailwind will result in a high approach speed and a long landing. Then there might be an overrun in combination with a wet and slippery runway.

Typicalexamples are: Airbus in Canada August 2006, Airbus Irkutsk July 2006, BAe 146Norway October 2006, Boeing 737 Java, 2007 and Airbus Sao Paulo July 2007.

Theproblem with Airbus is, that it is not possible to extend ground spoilers manually, as it is on other aircraft.

One disadvantage with a crash in tailwind is, that the fire will spread forward and reach your cockpit, as was the case in a tailwind approach with an Airbus in India February 1990.

Now type two accidents are becoming more frequent, as modern engines are spooling up much faster than older engines.

Tail Wind accidents in 2008

 Confirmed Tail Wind accidents

Jan 2                Run off the runway                                Type two accident

May 1               Run off the runway                                Type two accident

May 30             Run off the runway                                Type two accident

July 31             Run off the runway                                Type two accident

Typical Tail Wind accident but no windreport given

Jan 23                Landed short of the runway                Type one accident

Feb. 7                Landed short of the runway                 Type one accident

Feb. 8                Run off the runway                                 Type two accident

Feb. 13               Run off the runway                                Type two accident

Feb. 22               Run off the runway                                Type two accident

Mar 19                Run off the runway                                Type two accident

June 10              Landed short of the runway                Type one accident

July 6                  Landed short of the runway                 Type one accident

July 30                Run off the runway                                Typetwo accident

Aug 13                Landed short of the runway                Type one accident

Aug 27                Run off the runway                                Type two accident

Sept 13               Landed short of the runway                Type one accident

Nov 6                  Landed short of the runway                Type one accident

Running of the runway is the result when the aircraft is coming in “Hot and high” due to the tail wind and usually landing on a wet runway.

Landing before the runway will be the result when the pilot has managed to reduce speed to a“correct” value and reduced power, even more, when the tail wind abruptly was reduced and therefore speed increased closer to he ground.

It makes 12 percent of all accident in 2008

But normally, I guess, only 1% of all landings are made in tailwind