Alex,

No need for disagreement as there is no basis for that.

If my previous words infer that I am suggesting seat of the pants routine decision making as the aircraft is yawing wildly while passing through 150 KIAS or thereabouts, then I apologise ... for that was not my intent.

The thrust of my comments was directed to the concept that by rote application of technique (as developed in Bat Cave exercises) generally is going to give the most reliably desirable outcome .. but not always. The knowledgeable and competent pilot ought to consider (pre-takeoff) the whole picture and determine his/her plan in the light of all the information .. a bit like the CRM philosophy when utilising the resources at hand.

Very occasionally, it will be appropriate to change that plan in the heat of the moment if the day is to be saved .. for example ..

(a) if, under post-V1 failure conditions, the aircraft is departing the side of the runway (eg near certification Vmcg in a strong crosswind .. which can easily put the real world Vmcg above the failure speed), then it would be prudent (probably) to close the throttles and do the best one can to stay on the runway and accept the possible overrun .. in lieu of rolling the aircraft into a ball at much higher speed during the runway side excursion.

(b) the O'Hare DC10 engine separation accident may have had a very different outcome had the excess airspeed been exploited .. no criticism of the crew intended as they only had a fraction of the story with which to work at the time and made the best call they could .. but it is noted that the accident report suggested that the situation only needed a few knots to keep the left wing unstalled....

(c) if a control selection results in a strange response reselection to the previous setting may get one out of whatever the problem is. One is reminded that the TP fraternity generally subscribes to the "loud noise (etc) = keep things as they are .. at least it is still flying" approach to survival.

.. and a substantial list of such examples can be generated without too much difficulty ...

History is dotted with exceptional feats where the folk in the hot seat did wondrous things .. in the heat of moment .. by keeping cool heads and being innovative ... for instance

(a) the Sioux City DC10 accident which, by rights, probably should not have got that far in the first place. Al Haynes and his offsiders earned their collective career salaries that day ...

(b) the JAL B747 .. OK, the crew didn't have a happy outcome .. but they kept the bird in the air for a long time ...

Its an interesting argument, but does it apply when you are using assumed temperature thrust reductions?
Mutt

In that case, I agree with you. The VMCG accident will happen one day, I'm afraid, and the O'Hare DC10 crash could arguably have been avoided with better training. Your other examples show the profession at its best but, unfortunately, for every incident where the crew pull a rabbit from the hat you can find another one where they underperformed.

.. ah, and that is the reason that we push SOPs, standardised training, and practised by rote responses so much .. all a matter of running the stats and playing the numbers game. For every rule we can find exceptions .. and for every unusual, but desirable outcome, we can find a bunch of unfortunate stories ... no simple "win every time" answer, it seems.

I was tought to say "Veeeeeeeeee 1. Emphazis on 1, giving about a second to prepare for the decision. 1 being said exactly at the actual V1 speed.

Knold,

You risk falling into a common trap of trying to make V1 (one of many aspects of flying which fall into this category) operationally far more precise than is warranted by the technical reality.

If there is plenty of spare runway, the reality is that a modest speed overrun probably can be accommodated.

If the runway is accel-stop limiting then there is scant pad .. especially for pre-A/L 42 certifications. Add this to touchdown zone contamination at the stopping end .. grease ... oil .... did it rain a bit half an hour ago .. etc., etc. .. and you are near guaranteed an off-the-end event.

Risk assessment and minimisation in the real world is the aim of the game .. the certification gives a baseline from which to work but makes no guarantees unless the boundary conditions can be replicated in toto.

So far as calling V1 is concerned, it should be little more than "hey offsider, my ASI indicates that I am passing the precomputed V1 .. hopefully yours says the same ?" ... the other pilot should have been keeping a very close eye on his ASI throughout the takeoff. Hence there is little point in doing other than saying "V1" relatively normally .. but timing, I suggest, should be such that the verbiage is completed by the time that the needle is at the nominated speed.... and let's not get too bogged down by IAS/CAS concerns ...

The company I fly for wrote, tested, and implemented the Reduced V1 procedure described in the Boeing magazine article. We compute V1 normally and then subtract 8 knots. The V1 call is made at the new computed speed. There was a lot of doubt in the pilot ranks at first but after one high speed RTO at KLAX we all became believers. It was obvious that another 8 knots would have put them in the sand dunes off 25R. It is just normal to us now. Like Willit Run the majority of our takeoffs are max effort, on the edge of everything. We even do over speed takeoffs and aft cg takeoffs with reduced screen heights to get that last pound of freight. Factor in old airplanes, worn tires and brakes, 59 year old reflexes and the 8 knots becomes more attractive. If I were flying short haul high powered new generation aircraft I might feel different. But if you are operating on the edge of the performance charts it is something to consider.

Of course it is more attractive with a lower V1 when stopping is the concern.
Why do people always do this?
If you set your V1 lower than than the actual, what do you do if you get a cut between "your" V1 and the actual V1?
You will have comitted yourself too early.


John, I didn't mean to come of as some german efficiency/precision expert... :}

Mutt,

It certainly does apply when using assumed temperature takeoffs. When the runway is longer than required for the weight, the thrust is reduced using assumed temperature. In effect you are using more runway than you would at normal thrust settings and the speeds would then again be critical for that particular runway length and weight.

Boeing training manual states that the call V1 should be complete by the time V1 is reached.....now how slow or fast you want to make it is up to the PNF/PM :suspect:

The technology is now available to abandon the use of the IAS for the go/ no-go decision.

Ground speed from the IRS-GPS.
Remaining distance.

It would be relatively easy to integrate the enery management and present the pilot with an easy go-nogo decision feature.

I didn't mean to come of as some german efficiency/precision expert

Pass, friend ..

The technology is now available to abandon the use of the IAS for the go/ no-go decision

Been the case for a great many years .. but the ASI is still a simple predictor .. especially if one has runway marker boards or uses the stopwatch to monitor acceleration.

Cue barit1's thread on t/off acceleration monitoring? No time to search and maybe wrongly 'attributed'?

Surely at or around V1 on balanced field figures ie flex, If you really need to go, you can always push the throttles up, and you will get off the ground a lot quicker....

ah, but therein lies a trap. If the engine is not thrust limited by some other means, you have the option of overboosting and, potentially, adding to your woes by pushing the Vmcg/Vmca up to an embarrassing value .. depending on circumstances, of course.

Investigated one fatal where this (Vmca exceedance) was a very likely major contributor to the flight's endgame ... in general, it is possibly better to set and leave the thrust alone for the takeoff .. unless there is more to the problem than a simple failure.

Sorry J_T, although the takeoff can be continued at a Flex/Derated thrust, we specifically advise crews that they can increase Flex/Derate thrust to the maximum rated thrust at any time they desire. VMC values are therefore predicated at the OAT in order to provide the required protection.

KnackeredII,
Don’t you have a buffer provided when using Derated thrust? Is there a difference in performance when using an assumed temperature of 50C rather than an actual temperature of 50C?

Mutt

In connection with Mutt's question.


http://i47.photobucket.com/albums/f1...r/e974cdf8.jpg

I'm sorry to say I didn't quite understand the table. Is the difference in IAS vs TAS due to temperature alone?

Mutt, in answer to your question, yes, there is a performance difference when using an assumed temperature of 50 deg versus full rated thrust when the actual oat is 50 deg.

For example, on a 50deg day for the CF6-80, the N1 is 106.3%. On a 25 degree day, derating to 50 degrees gives a figure of 102.1%. Why? Because even though you have derated the thrust, the fan still has to spin in the air density of the 25 degree day. The EGT to spin the fan at 106.3% on a 25 degree day would exceed the Takeoff thrust EGT limit.

Sorry to get off topic, but the question was raised...:)

I don't believe it 'better training' would have changed it. I believed the crew performed as they were trained.

There were multiple issues.. 1) the procedure they used as did many at that time was to climb at V2 or V2+20 as max speed and if you were above that speed, you increased pitch to reduce speed back to V2+20. 2) they were not aware that there was no lock-out with a hydraulic failure and when the hyd failed, the slats retracted. The combination of those factors, as I remember, created the roll for which there was insufficent control.

Both problems were addressed in the post crash findings.