Jump to content
Sign in to follow this  
wde12

Early Runway Entry Point Procedure

Recommended Posts

This is an interesting topic that seems everyone has an opinion on. I don't personally see any problems with an intersection departure if all the calculations check out. The Qatar incident, as with so many accidents, was a series of errors, a chain if you will, that led to this happening. If I can compare with the Emirates A340-500 incident at YMML a few years ago, they used the full runway, but entered a takeoff weight about 100,000kg (yes, 100 tons!) less than the actual. If they had tried to abort at close to V1 they may very well have gone off the end as well. (thankfully they continued into the air, and took out some approach lights as a souvenir, as well.)

 

Here in NZ, the smaller regional airplanes regularly do intersection departures at the bigger airports, as a passenger (and reasonably well informed aviation enthusiast) I would groan at the thought of my ATR72 flight trying to use a full length takeoff at Auckland (12,000ft) or Christchurch (10,800ft) as it would add ages to the taxi distance. In fact, on runway 05R at Auckland, the "extension" which is really a displaced threshold requiring backtrack and a 180deg turn, is only available at prior request from ATC during clearance delivery. A lot of big jets don't need or use this when departing off 05R, and they make an intersection departure from A10.

 

In the Qatar case, they may have been able to achieve the exact same (almost catastrophic) flightpath by using a full length with erroneous weight or derate calculations, making the intersection departure a moot point.

 

Point is, as Kyle said, they made a miscalculation and lost situational awareness. The intersection departure was merely a contributing factor in the chain of events.

 

I think for airlines, it is a balancing act of shorter flight time using an intersection vs decreased engine wear using full length with a bigger derate.

 

If you wanted to take the Jims point to an extreme, why don't we not only use full length at all times, but also full rated takeoff thrust. Why not? Because aviation is a balancing act between safety and economics and sensibility.

Share this post


Link to post
Share on other sites

Jim,

 

Let me offer an alternative situation.

 

You calculate your fuel requirement for a trip according to the regulations and load it. You take off (using the full length!) and proceed enroute.

 

Shortly before arrival, an unforecast fog bank descends over your destination and forces you to enter a hold whilst you wait for it to clear up.

 

If you'd taken off with full tanks instead (bearing in mind nobody had predicted the fog), would that have been more or less safe in that situation? As you might come across unforecast weather at any point, why not enhance your safety margin by topping the tanks off every time you depart? Why would you knowingly choose to reduce your options by not brimming the tanks before every departure?

 

Hello, Simon,

 

You takeoff from your departure point and upon arrival at your destination, you are surprised by unforecast fog, preventing your being able to land straight away. If you performed your preflight fuel loading appropriately, would this present a problem or a safety concern? Bear in mind if you would, my primary destination doesn't necessarily mean my final destination.

 

"Folks, we are now having to divert to our alternate destination due to "unforeseen" weather present over our destination. They are telling us that the weather isn't going to improve any time soon. Please sit back and enjoy the next (fill in the blank) minutes while we fly to our alternate destination."

 

     Would you need to top off the fuel tanks before each departure to accommodate for the probability of not being able to land at your initial destination?

     How are your flight planning capabilities?

     Did you do due diligence enroute and check for weather updates for your destination and alternate airports?

     What was, and while checking enroute, is, the T/DP currently and trending at your primary and alternate destinations?

 

"Why would you knowingly choose to reduce your options by not brimming the tanks before every departure?"       Landing weight restrictions come to mind.

 

Personally, I choose to properly preflight my trip and it's fuel requirements. Do I reduce my options by not brimming the tanks before every departure? Of course options are reduced.

 

If I'm at my ETP over the ocean, wouldn't it be better to have more fuel available, especially if the pressurization system fails or an engine fails? But, since there are times when full tanks aren't an option, wouldn't it be nice to properly preflight the fuel requirements for the trip and know that you have the fuel on board for most known and common unexpected events? Short of a major fuel leak in the system. Which could never happen on an AirBus out of Canada.

 

The real question is will the reduction in options of not flying every flight with full fuel tanks get me killed? So far, not in over 40 years of worldwide flying. Hopefully, the next 40 years of flying will yield the same results.

 

So, alternatively Simon, back on topic:      Why would you knowingly choose to reduce your options by not using the full length of the runway for every departure?

 

Were the two recent 777 engine failures at KLAS and KFLL, before runway lineup, safer for passengers and crew in the aircraft? Would the passengers and crew be as safe handling the engine failures during a departure if instead of using full length an intersection departure was used instead? Or, would the safety factor be the same for both an intersection departure and a full length departure?

 

Is it safer to depart from a runway and do so leaving 300m of runway behind you from your starting point of the takeoff roll? Leaving 300m less available runway off the nose during the takeoff roll? Especially if all of a sudden you realize that the aircraft isn't performing as expected because of fouled data entry input. That neither the Captain nor co-pilot caught (Cross-Checking). Could this ever happen? 

 

Would having just enough runway for departure be safer than having all available runway remaining for departure?

 

Was the MadDog departing not long ago out of KLAS safer when they aborted takeoff AFTER VR following a loss of flight control during a full runway departure if they would of opted for an intersection departure? Go off the end of the runway or try to fly the crippled aircraft. Pretty bad set of options to have to pick from after making a poor takeoff operational choice. Fortunately, the flight crew made the safest of the two choices before takeoff. Their decision gave them more runway available for takeoff, than just enough runway available, which allowed for a successful post VR abort and stopped the aircraft on the remaining runway. Our boxes do not take into account "Runway Required" for an abort at or after VR. As the FAA puts it "You become test pilots."

 

Cheers,

 

Jim Wilkerson

Share this post


Link to post
Share on other sites

Hi Jim,

 

     How are your flight planning capabilities?

     Did you do due diligence enroute and check for weather updates for your destination and alternate airports?

     What was, and while checking enroute, is, the T/DP currently and trending at your primary and alternate destinations?

 

 

If I'm at my ETP over the ocean, wouldn't it be better to have more fuel available, especially if the pressurization system fails or an engine fails? But, since there are times when full tanks aren't an option, wouldn't it be nice to properly preflight the fuel requirements for the trip and know that you have the fuel on board for most known and common unexpected events?

 

And here is the point. You accept the reduction in options that taking off with less than the maximum possible fuel gives you (whether that's brimming the tanks or taking advantage of the underload vs MTOW or MLW to load extra fuel up to that limit) because in the planning stage you have weighed up the options and possibilities and selected a fuel load that you believe will cover you for "the most known and common unexpected events". As you freely admit, there are occasions where it would be nice to have more fuel on board. But you accept the elevation in risk should that circumstance occur because you have carried out your due diligence in flight planning. Even so -- there was a BA 777 at EZE a couple of years ago that ended up landing below minima because in the event they did not have enough fuel to divert (and the diversion fields had also gone below minima in any event). I am sure that the crew on that flight did their due diligence and loaded what they thought would be sufficient fuel to cover them for the unexpected events they would encounter, and yet still found themselves in a situation where they were short of fuel.

 

And if someone does not do their fuel planning correctly, or the refueller loads the wrong amount of fuel and the crew don't notice, and as a result they run out -- following your logic the argument would be that if they had simply loaded the maximum possible amount of fuel then the accident wouldn't have happened.

 

In the same way, when one carries out an intersection departure one carries out due diligence in calculating the takeoff performance. Just like the regulations around fuel planning, the takeoff performance calculations are designed to take in to account the most known and common unexpected events. If you subsequently enter the wrong data, or take off from the wrong runway or with the wrong flap setting then as you say you have become a test pilot, whether you are using the full length or not. And just like fuel planning, there's nothing stopping you from adding in an extra margin if you wish by calculating the performance from an even shorter intersection than that which you plan to depart from if so desired.

 

To answer your question directly -- why would I not necessarily use the full length of the runway every time? Crossing traffic, for a start. If I have the option of starting my takeoff roll a few hundred metres further up the runway and by doing so avoid having to cross an active runway at high speed during the takeoff roll, a situation which potentially puts me in to direct conflict with another aircraft should any of the parties involved -- me, ATC, the other crew -- make an error, then that is a significant reduction in risk provided I am using the correct performance data -- which, as I say, goes for any departure, full length, intersection or otherwise.

 

Would the passengers and crew be as safe handling the engine failures during a departure if instead of using full length an intersection departure was used instead?

 

Provided they were using the correct performance, then absolutely. Why wouldn't they? That is exactly the scenario that the takeoff performance calculation is predicated on.

 

If they had been departing from BOS 22R (TODA 2397m) would that have been less safe? If I were to depart from A7 on 27R at LHR, conversely, TODA = 2574m. Should I refuse to depart from 22R at Boston? By your reckoning it must be inherently unsafe. Or is it safe because I have used the full length, even though the full length there is less than an intersection at LHR?

 

To take it to an extreme -- should I refuse to ever depart off 27L at Heathrow, because 27R is 300m or so longer? That would give me even more options in the event of an unforeseen problem, wouldn't it?

 

Best,

 

Simon

Share this post


Link to post
Share on other sites

We've been through this in a prior thread. It's very clear that the one argument is less about actual safety and more about some misguided idea of what acceptable risk is. The original question was answered. There's no need for this thread to be used as a soapbox for tangential ranting.


Kyle Rodgers

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...