Wednesday, 22 July 2009

EK407 Tailstrike


Anyone heard about this? Back from March 2009. Media very quiet.

www.pprune.org

11 comments:

PH said...

full report :

http://www.news.com.au/heraldsun/story/0,21985,25766891-661,00.html

Found it on the forum you linked to. If you read the forum it's funny how they start out mocking Arabs and Muslims and saying it was ultimately the pilots fault even if he wasn't Arab; but in the news report ( after it was determined that it wasn't an Arab ) they start out with saying he saved the passengers and only admitting it was his fault at the end of the article :)). They wouldn't even mention his nationality, only said he was European !

BuJassem said...

Thanks PH, but never trust the media for technical information. I am an aviation enthusiast and prefer to get my information from official sources like this one below:

http://www.atsb.gov.au/publications/investigation_reports/2009/aair/aair200901310.aspx

You can scroll down and download the full (interim) report which is a pdf under 5mb. The pictures are good and they focus on the aircraft and they avoid naming the carrier, Emirates; or the flight number.

I read the mocking remarks about how the Captain is automatically at fault etc and how he's probably running to get his family out of the UAE etc. To be honest we do not cover ourselves with glory in how we treat foreigners, so we kinda deserve it. Can't really defend it.

Back to a technical viewpoint, the ATSB indicates the problem as that of a lack of thrust. When you take off with modern aircraft you rarely use 100% of engine power. If the plane is below it's maximum takeoff weight, you could get away with using 80% or 85% of the thrust. This saves fuel, noise, and engine wear-and-tear. Remember that the takeoff is the most dangerous part of any flight since your aircraft is at it's lowest altitude, at it's lowest speed, and at its heaviest.

Anyway, so the crew (captain & 1st officer) underestimated the plane weight by 100,000 kg, which fed into the laptop and thus the controllers of the airbus to use a lighter thrust, which meant the plane did not have enough speed by the time it reached the end of the runway.

There could be another secondary problem such as the piezotubes that indicate airspeed could be blocked and this gives an inaccurate airspeed reading. This affects V1 and Vr. V1 is decision speed (when you reach it, approx 140 knots) you cannot abort takeoff. Vr = rotation speed, and that's when the captain should lift the nose (Vr can be approx 170 knots etc). All this depends on the aircraft model and the flaps and the weight and runway length , wind, etc..

rosh said...

BuJ - thank you for explaining really well, especially the co-relation between aircraft weight, its speed and engine power. Quite interesting stuff. Q: what if the aircraft speed is at a high (i.e. the opposite of this incident)? Is that a good thing? I ask because, often in business travels across the North / South America - the flights are full. The domestic flights are often full (seats and the overhead baggage) and the passengers (read Americans) are rather heavy - hence often (and this may sound silly) I worry if the aircraft will take off fine. Also what is the heaviest part of an aircraft? Is the tail heavy? I read somewhere the strongest part of the cabin is where the wings are attached.

I wanted to be a Pilot (or a Jurno) However, my folks (read mom) forced me into having a "real" job. So I'm a CPA, with an MBA, crunching numbers and making corporate ...OK, useless info, that... :)

rosh said...

WOWza! wallah comment moderation? :)

BuJassem said...

Dear Mr Rosh!

Lovely to read ya!

I'll try to answer your various questions.. but please correct me because I don't think i understood all of them!

Q1: " what if the aircraft speed is at a high (i.e. the opposite of this incident)? Is that a good thing? "

A1: Well my friend, all you need for flight is basically LIFT.. lift acts opposite to WEIGHT and makes flight possible. Wings produce lift by the flow of air, and hence the more air (i.e. speed) the better the lift.

So to answer your question, when you take off (since you want to gain altitude) the more speed the better, and to do this, sometimes you need a longer runway for bigger planes (e.g. B747) or those that are heavily loaded.

Now, the opposite is true when you land, you want to land at the lowest possible speed. However there is always a catch. If the plane is too slow there won't be enough airflow and hence enough lift. This means that WEIGHT will exceed LIFT and the plane will fall from the sky (aka called a stall). This forces the captain to increase engine power >> more speed >> more lift. Also, to make it more scary, the slower the airspeed the less stable an aircraft is and is more susceptible to gusts of winds and so on, so the captain has to draw a fine line between too slow and losing control and too fast and running out of runway. Sometimes in emergency landings the pilot goes for a high speed landing as it makes the aircraft more controllable in the air.. but it means he will probably run out of runway. however if you think about it, it's the lesser of two evils. The speed of a plane at the end of the runway will be approx the speed of a normal car, maybe 50 mph. Thus the threat to life will be minimal. However if you crash at the beginning of the runway, you'll be doing in excess of 200-300 mph depending on the plane.. and that will hurt much more!

As a final part to your answer.. the takeoff is ALWAYS the most dangerous part of any flight. This is because the weight of the passengers + full tanks of fuel (which can be more than 100 tons!) means the aircraft is at its heaviest. Also the engines will be working at 100% (usual flight means the engines run on 80% or so power).. this increase on power from 80 to 100% is very taxing on the engine.. and means things can go wrong. If you lose an engine during crusing you can land safely,, but if u lose an engine during takeoff you'll most probably die (remember the concord crash in paris?). Flight is so safe, but the time when I really say my prayers is the takeoff!

Q2: Also what is the heaviest part of an aircraft? Is the tail heavy? I read somewhere the strongest part of the cabin is where the wings are attached.

A2: My friend there is no "heaviest" part of an aircraft because engineers spend YEARS to make sure the weight is spread evenly. This includes the structure but also fuel, passengers, cargo etc.. Actually there are very sophisticated engineering behind the fuel tanks because of the great weight of fuel. Like I mentioned this can be in excess of 100tons.. which in my simple maths can be 40% of the weight of the plane. (in a car the fuel is less than 5% of the weight). Anyway, the centre of mass of the plane is designed to be where the wings meet the body of the plane. That is also the stiffest part of the structure. However the safest part of a plane when it crashes is the rear. that's where they put the black boxes.

If the tail is heavy or then the plane will point to the sky and stall > crash. If it's nose heavy it will never be able to take off.. So you need the centre of mass to be in the centre of the aircraft.

sorry this is a bit long but hope it helps. also apologies for the moderation but it's coz i had an unwelcome guest. however you are always very welcome my dear friend :)

Dubai Jazz said...

YAY! Bu Jassem is back!

Tayyeb ya rayyal, la 7es wa la khabar????!

I find this incident quite interesting.

Like Mr. Rosh, I have a question of my own.

Q1. is there a universal speed upon which any plane can take off? i.e. is the take off speed (and consequently, V1 and VR) correspondent to the weight of the aircraft?

BuJassem said...

welcome ya DJ!!! so how did u find my blog then? hehe

i didn't publicise it to see if ppl will find out themselves and also if i want to delete it after a few days i won't feel i let you guys down!

to answer your question, there is NO universal takeoff speed, but there are universal speed notations.. just like almost all buildings have gridlines, not all buildings have the same gridline spacings.. you know.. either a 5000, 7500, 9000 mm grid.. depending on use etc.

weight is a strong factor when determining V1 and Vr, but there are other factors such as:

1- wind speed (weather)
2- flap position (more flap > more wing area > more lift) this means that the plane will lift off at a slower speed, which is good.
3- type of aircraft/engine installed.

there are other lesser important factors such as airport location and so on. Sometimes (like the old HK airport) there were big mountains near the airport, so the captain will probably use the runway to the max to increase speed before he takes off.. thus meaning he can climb faster and clear the mountains after it.

it's EXACTLY like if you're in an enoc station on emirates road and u want to join the motorway.. if you use 20% of the slip road, it probably means your speed in the motorway will be around 50 or 80 kmh and the trucks will crash into you or honk and brake.. but if u use 80 or 100% of the slip road (aka runway!) then you can reach 100 or 120 kmh easy and merge with ease. hope it makes sense.

safe flying and driving!

Dubai Jazz said...

Mukhabarat habeeb, we know everything :)

Seriously, I was just clicking idly around. It was a pleasant surprise.

Take it easy. It's supposed to be a pleasure. Hope you'd continue writing.

Dubai Jazz said...

And btw, Bu Jassem, your blog is still on my blogroll, which hasn't been updated in ages.


And also, I had a hunch you'd come back. So there.

BuJassem said...

speaking of which, i noticed i'm on your twitter page and the biggest ba3boos is that you're using WINDOWS on a MAC machine!!! how awful.. how terrible?!!!!

please don't say mukhabarat here.. we're at a higher level.. you know.. NSA, Homeland Security, MI6, etc.. hehehe

u know, i have so many things to say.. esp with my new job, but otherwise they would kill me and my family! but this place is a doggy dogg city!

3ala fikra.. i need to rebuild my blogroll.. give me some time.. :)

Dubai Jazz said...

Bu Jassem,

It wasn't me. I certainly don't own a Mac!