Tomorrow I'm planning on flying from Bern LSZB to London EGLL, there is a Vatsim event in both places tomorrow evening so should be quite a good flight.

So what was your setup for takeoff and how did it turn out.

Bleeds on, flaps 25 take off. V speeds where around 130, 131, 140 (something around there anyway)

 

It went fine, though rotation was near the end of the runway which was certainly more exciting then the miles I usually have a head of me. Places I have flown always seam to have pretty long runways, landed at Gib once but never flew back so maybe I should try that. Or just fine more small airfields

 

Overall, pretty successful. But I'm going to try it again with Bleeds off and less flaps and see what difference it makes

Yep just as long as you remember what stearmandriver said - it's also important to leave yourself some room on the runway for a failure before V1. But I mean, in FSX you're going to know if you're going have a failure anyway so you might aswell use the entire length. This is where the ngx really shines, because you can plan failures, and do the associated QRH c/l items. Very cool, especially at places like LSZB.

 

To Kevin - of course I don't conduct a brief... i mean seriously! Lol. But I suppose we differ on the point whether you'd brief it or not. But I gotta say, I like stearmandrivers point of briefing anything that's not normal.

I think that if I had a problem up to V1, I wouldn't stop it time. Maybe around 60 it would be ok, but 110, 120 I would have been off the end I think. To that end, maybe bleeds off would have given me a little extra and more breathing room. I'll run the numbers through Topcat and see what my margin is.

 

One thing I'm struggling with this, is if flaps add drag but increase lift, then on takeoff this results in a lower rotate speed but slower to get there. Is that correct? Because I can't work out what's the lesser of two evils in this situation

For shorter runway, more flaps helps. If you've got climb restrictions, then less flaps is better.

Ok, so running the numbers with a few different options it would be best for bleeds off to give as much margin as I can running around half full on weights. Topcat does give a recommended Derate, but given the small margins I'm not sure how safe that would in the real world;

 

Bleeds On:

 

TAKE-OFF LSZB/BRN  RWY 32  TORA 5676FT            
EI-FEF  BOEING 737-800 CFM56-7B26
BELP                                              

TEMP +34C   QNH 1014   WIND 310/06 (05KT HW)

------------------  CONDITIONS  -------------------
TOW 60374 KG   FLAPS 25   THRUST TO   RWY DRY
AIR COND ON   ANTI ICE OFF

------------------  FULL THRUST -------------------
  +34C  62370 FIELD    133   133 133   315FT  99.7%

----------------  REDUCED THRUST  -----------------
  +35C  61960 FIELD    133   133 133   252FT  99.6%
  +36C  61553 FIELD    133   133 133   191FT  99.4%
  +37C  61170 FIELD    133   133 133   132FT  99.2%
  +38C  60787 FIELD    133   133 133    71FT  99.1%
//+39C  60404 FIELD    133   133 133     7FT  98.9%

 

 

Bleeds Off:

 

TAKE-OFF LSZB/BRN  RWY 32  TORA 5676FT            
EI-FEF  BOEING 737-800 CFM56-7B26
BELP                                              

TEMP +34C   QNH 1014   WIND 310/06 (05KT HW)

------------------  CONDITIONS  -------------------
TOW 60374 KG   FLAPS 25   THRUST TO   RWY DRY
AIR COND OFF   ANTI ICE OFF

------------------  FULL THRUST -------------------
  +34C  62770 FIELD    133   133 133   377FT 100.6%

----------------  REDUCED THRUST  -----------------
  +36C  61953 FIELD    133   133 133   254FT 100.3%
  +37C  61570 FIELD    133   133 133   197FT 100.1%
  +38C  61187 FIELD    133   133 133   136FT 100.0%
  +39C  60804 FIELD    133   133 133    73FT  99.8%
//+40C  60422 FIELD    133   133 133    10FT  99.7%

 

 

Given my knowledge, which is only sim knowledge, I'd prefer more margin so select bleeds off and no derate

I think that if I had a problem up to V1, I wouldn't stop it time. Maybe around 60 it would be ok, but 110, 120 I would have been off the end I think. To that end, maybe bleeds off would have given me a little extra and more breathing room. I'll run the numbers through Topcat and see what my margin is.

 

One thing I'm struggling with this, is if flaps add drag but increase lift, then on takeoff this results in a lower rotate speed but slower to get there. Is that correct? Because I can't work out what's the lesser of two evils in this situation

 

Assuming the calculations are correct, if you initiate the first action to stop by V1 you should stop within the ASDA. However, any high-speed reject, especially on a limiting runway, is a challenge and requires everything to be done extremely promptly and correctly. Of course, it's all dependent on the NGX flight model being accurate to the real thing under those circumstances.

 

Remember that where you rotate and get airborne is inconsequential: it's the V1 call that's significant. I have to say, I never really appreciated takeoff performance until I moved to the 747: twins are generally very overpowered (remember they have to cope with a 50% loss of power in the event of an engine failure, whereas an engine failure in a quad only removes 25% of available power) and the higher weights, speeds, bigger splits between V1 and Vr and more limited climb performance make you realise the criticality of those calculations!

 

You're right about flaps -- but the concern about extra drag is more to do with climb rate than acceleration on the runway. A higher flap setting will result in a shorter takeoff run, but will also result in a lower rate of climb once airborne (rate of climb is directly related to excess power: any extra drag will mean some of that excess power is devoted to overcoming the extra drag, so a lower climb rate will result. This is also the reason why climb rate diminishes in a turn). So you're not trading off against takeoff run: you're trading off against obstacle clearance (or required climb gradients) further down the line.

Ok so that's fine then since I had no problems with alt restrictions, but good to bare in mind for other airports. Some in northern Italy need a rapid climb to get out.

 

So for this case, the fact it's flaps 25 doesn't mean anything since climb rate will be fine, even if lower. What is important is runway length to stop up to V1. The V1 speed didn't seam as if it was lower because of the short runway length. I don't know if that is reflective of real life, or simply Topcat doesn't take that in to consideration, but I wonder if reasons for an aborted take-off would be less because of the short runway an aborted take off is far riskier.

 

But, even so, that does lead to me suggest that since flaps are not an issue here it's runway margin, so I presume dispatch surrounds highest weight for profit vs what is safe (which my calculations come to just over half load) and using bleeds off to increase the tiny margin I have.

 

At this point though, I am way beyond the "flight sim" world of flying a plane and going deep in to the rabbit hole of dispatch! Not that I mind, it's been a good learning exercise to really get to know the plane. Learnt far more then taking off at EGLL which has enough runway for a heavy A380!

Ok, so running the numbers with a few different options it would be best for bleeds off to give as much margin as I can running around half full on weights. Topcat does give a recommended Derate, but given the small margins I'm not sure how safe that would in the real world;

 

Bleeds On:

 

TAKE-OFF LSZB/BRN  RWY 32  TORA 5676FT            

EI-FEF  BOEING 737-800 CFM56-7B26

BELP                                              

 

TEMP +34C   QNH 1014   WIND 310/06 (05KT HW)

 

------------------  CONDITIONS  -------------------

TOW 60374 KG   FLAPS 25   THRUST TO   RWY DRY

AIR COND ON   ANTI ICE OFF

 

------------------  FULL THRUST -------------------

  +34C  62370 FIELD    133   133 133   315FT  99.7%

 

----------------  REDUCED THRUST  -----------------

  +35C  61960 FIELD    133   133 133   252FT  99.6%

  +36C  61553 FIELD    133   133 133   191FT  99.4%

  +37C  61170 FIELD    133   133 133   132FT  99.2%

  +38C  60787 FIELD    133   133 133    71FT  99.1%

//+39C  60404 FIELD    133   133 133     7FT  98.9%

 

 

Bleeds Off:

 

TAKE-OFF LSZB/BRN  RWY 32  TORA 5676FT            

EI-FEF  BOEING 737-800 CFM56-7B26

BELP                                              

 

TEMP +34C   QNH 1014   WIND 310/06 (05KT HW)

 

------------------  CONDITIONS  -------------------

TOW 60374 KG   FLAPS 25   THRUST TO   RWY DRY

AIR COND OFF   ANTI ICE OFF

 

------------------  FULL THRUST -------------------

  +34C  62770 FIELD    133   133 133   377FT 100.6%

 

----------------  REDUCED THRUST  -----------------

  +36C  61953 FIELD    133   133 133   254FT 100.3%

  +37C  61570 FIELD    133   133 133   197FT 100.1%

  +38C  61187 FIELD    133   133 133   136FT 100.0%

  +39C  60804 FIELD    133   133 133    73FT  99.8%

//+40C  60422 FIELD    133   133 133    10FT  99.7%

 

 

Given my knowledge, which is only sim knowledge, I'd prefer more margin so select bleeds off and no derate

 

The V1, VR and V2 speeds are all the same.  TOPCAT is giving you bad data, as least as the speeds are concerned.

hmm true, however I was only messing with the numbers at this point. When I did my real flight I saw 130, 131, 140 or there about. V2 was definitely 140 and VR was 131

 

I wouldn't take those as good numbers but was more interested in the margin column

So for this case, the fact it's flaps 25 doesn't mean anything since climb rate will be fine, even if lower. What is important is runway length to stop up to V1. The V1 speed didn't seam as if it was lower because of the short runway length. I don't know if that is reflective of real life, or simply Topcat doesn't take that in to consideration, but I wonder if reasons for an aborted take-off would be less because of the short runway an aborted take off is far riskier.

 

Bear in mind that V1 isn't just all about stopping -- it's also about going. If you have an engine failure at V1 + 1kt, you still have to be able to accelerate to Vr on the remaining engine, take off and reach the 35ft screen height at V2 within the TODA. So it's a balancing act: a lower V1 will give you more room to stop, but will also require a greater distance to go in the event of an engine failure just above V1.

 

Edit: just to follow up on the second part of your question -- the reasons for rejecting remain the same. A high-speed reject on any runway is an inherently risky event: hence why manufacturers and airlines tend to divide the takeoff in to low-speed and high-speed regimes.

 

At low speed (as far as Boeing is concerned - up to 80kt) you would generally stop for any significant malfunction or safety-related warning, or anything that generates a master caution.

 

Above 80kt, the risks involved in rejecting start to increase, and for this reason you would normally only stop for fire, an engine failure confirmed by two or more parameters, a windshear warning or configuration warning horn, or anything which causes you to believe the aircraft will not fly (jammed controls, for instance).

 

The way I seem to recall Boeing putting it in the FCOM is:

 

"A decision to reject is not made because it is possible to stop: it is made because the aircraft will not fly." 

 

Most of the time it is safer to deal with the problem in the air and return for a landing if necessary: that goes for any runway, not just limiting ones!

 

 

At this point though, I am way beyond the "flight sim" world of flying a plane and going deep in to the rabbit hole of dispatch! Not that I mind, it's been a good learning exercise to really get to know the plane. Learnt far more then taking off at EGLL which has enough runway for a heavy A380!

 

It's not really all about dispatch: pilots still have to have a thorough understanding of the factors which impact the performance of the aircraft and the regulations and safety margins that are built in to the takeoff performance calculations. Whilst EFB-type calculators are becoming fairly ubiquitous, it's not unheard of for airline crews to have to do the calculations themselves with tables and vital data cards either. Yes, payload restrictions may have been calculated in advance, and there may be certain SOPs for particular airports, but most of the time there is more than one solution available. In those cases, it is up to the crew to know what the limitations are in any particular situation, and how to optimise one aspect of performance or another.

Hi,

last week after having seen videos about Skhatos takeoff (both A320 and B737) LGSK( runway lenght= 1650 meters) I tried that: I remember that last year an Italian Air Company whose virtual "real related" company I'm flying for was operating a (teorically) non-stop LGSK-LIMC flight . But when I asked (via my real related virtual company) how , during strong headwind day(usually we got always headwinds flying from Greece to Italy), could perform a non-stop flight without penalizing too much the load factor they replied than sometimes a refuelling stop to Thessaloniki (LGTS) was necessary.

So I programmed a short hop LGSK-LGTS using both a B737-800 and B737-700 under those conditions:

 

Flaps 25 bleed off takeoff;

T.O. bump engine power (27.3K pounds)

RTOW (Reduced takeoff weight) based on TOPCAT with a margin of 200-300 meters anyway:

fuel=4200-4300 kg (short hop to LGTS about 110 miles plus 2,5 tons reserves so I saved my load factor...)

But naturally before operating this flight I executed a couple of (before) V1 cut (no go).

I used Fsipanel but the problem was "to tune" the speed to trigger the failure...having a V1 of (about) 125 kts I had to select a value of about 113-115 kts to "feel" tha failure at 122-124 kts (in such RTOW and TO BUMP condition you got a very fast acceleration in fact your weight to thrust ratio is equal if not better than that one of a Concorde).

So my advice is : before trying a short runway takeoff  to have a little training about before V1 failures...

Best

Andrea

I've seen actual takeoffs where the end of the runway sure looked too close to stop, yet the numbers said it would work. Don't underestimate RTO autobraking if you've never seen it ;-). I've never tried a high speed abort in the NGX; think I will now. But if it's accurately modeled, it's impressive. Why not try your takeoff that started this discussion again, at same weight and environmental parameters, and thrust and flap settings, but reject at V1? See what happens. The ability to experiment is what makes a sim fun!

Yes I will, I want to try the take off a few times with some different weights, bleeds and flap settings and see what happens in real sim life, rather then what Topcat tells me. Part of the great aspect of being able to do this easily from home.

 

Andrea I might try that flight myself. I've recently got some better Italian and Greece scenery so I have been meaning to fly to both places more.

 

I was with BAv however they have so few 737 flights now (and soon none) and of those, none of those where particularly challenging so ended up leaving. I'm not a Busser so the other routes have no interest for me. But I'm with vRYR and I know they fly to some odd places (their "Oslo" airport is an interesting one depending on the wind).

 

But, as you say, best thing to do is try and V1 aborts and see what really happens. Without that, I'll never really know since I've never had a service based takeoff incident

Hi Chris,

you right: V1 cut are really very interesting...

the first problem here is that w/o a software like fsipanel, using just your standard ngx failure menu (don't misunderstand me: it's a great tool with a lot of realistic failures that can be simulated)but you can't program an indicated airspeed from which failure is triggered and by using standard "v1 cut failure" at RTOW and TO BUMP when you realize that your engine has failed (i.e. 2 second later) you've overpassed v1 and you're committed to fly (anyway very interesting having in your SID bound to Thessaloniki a 6000A constrain at a near waypoint that in this moment I can't remember  and with one engine out you'll have to program an holding over there to reach that altitude...) 

Anyway very interesting..I prefer to keep some margins vs TOPCAT calculations (i.e. I require a margin never less than 200-300 meters otherwise I reduce my weight) because as Joe have said TOPCAT is not always correct (naturally you'd use a real air company takeoff calculator software to have precise data (valid for real airplane in that company's configuration).

Ciao

Andrea