Since my earlier posts, there seem to have been a few questions pointed my way, good manners and a healthy interest in PPRune’s best ever running thread compel me to reply. I’m still on leave, so perhaps the replies are a little disjointed and out of time synch.
Centaurus, my reference to the pilot being like a coiled spring approaching V1 was in the vein of being MENTALLY like a coiled spring, the decision must be made and executed in a very short time indeed. There’s nothing symbolic in removing one’s hands from the thrust levers at V1, it’s a positive action to prevent the inadvertent ‘knee-jerk’ Thrust Lever closure by the ‘mentally coiled pilot’ when hearing the V1 or Rotate call. It was my own discipline to do this long before it became a SOP, my own mental preparation was “We are going to Reject”, before V1 was reached, immediately becoming “We are going to Continue” when V1 was called, as I raised my hand from the Thrust Levers. Your description of some pilots with a vice-like grip on the Thrust Levers is a bit worrying.
No problem with V1 and Vr being the same figure, simply call Rotate”, and dispense with the V1 call, it’s now redundant anyway. A little akin to my suggestion that there is a case for replacing the V1 call with a
GO call. (We did this (the Rotate call that is) on the B727).
SR71, Yes the very long runway far in excess of requirements does pose a philosophical argument making an abort decision above V1 more acceptable. I have had the “pleasure” of an abort above V1 with a complete control jam, but the runway was some 2000M in excess of that required. All of my fore-going arguments have related to the aircraft being Field and/or obstacle limited, if both of these are spare, then there is no problem, but the pilot has no way of knowing just what is to spare, and therein lies a problem.
A further major problem is that when there is field length “to spare”, we then make it limiting by using Flex / Assumed Temperature thrust, making every takeoff a limiting one. A reject above V1 when using Flex / Assumed Temperature thrust would be most inadvisable. And 'one for the road', does your reject above V1 consider Vmbe?
SIDSTAR, a good post, you make several good remarks –
(1)
”Stick to your company's script and you will not go far wrong. If you are unhappy with the SOPs try to get them changed”. Yes, we could make every V1 equal to Vmcg (or Vmcg plus a bit for comfort) if we wanted (I wouldn’t), it would cost a lot of money from Boeing, Airbus et al, because then the continued Takeoff would become much more limiting, and have to be re-certified at great expense.
Denti, I think that your new owners would have had to do this when they introduced the new much lower V1s, at least I hope that they did! Balanced Field principal would be thrown out the window (now that’s a good idea,
J_T may agree, but
Mutt is a much more balanced individual).
(2)
”Boeing did a study some years ago on the amount of braking applied in RTOs by a range of pilots ranging from their own certification test pilots to the average line guy. It was interesting that the only group who consistently used the max braking available to them was the test pilot group”. There are three ways to fly an aircraft – (A) Smoothly and accurately (Normal line flying), (B) Assertively (Engine out, show the aeroplane who’s boss, but as accurately as possible), and (C)
Aggressively, using maximum effort and adrenaline. RTO Brake application and collision avoidance fall into the latter category.
Richjb, I think that you said it all. Some good extra points arise from your discussion.
“critical engine failure speed” this is a misnomer”, heartily agreed, it might have been good in it’s day, but if we’re looking for a realistic critical engine failure speed, then look to Vef. That’s where the process begins. Nor is it the ‘Decision Speed’, by the time that V1 has been called, the decision has already been made, back at Seattle, Toulouse, Wichita, et al.
I think that your best remark was
“Understanding the differences between and more importantly the limitations inherent with these certification rules is necessary for pilot to completely understand V1 & accelerate-stop distance”. It is
VITAL for a competent operating pilot to fully understand and comprehend the basis upon which the performance criteria have been created. FAR 25 (and all of it’s equivalents) is an unusual piece of legislation. It is the law, but an unusual law in that it is also the criteria by which the Performance Engineering folk generate the real-world data with which we comply. In most instances in life we stay within the law, in the FAR 25 case, we take the law all the way to the limits.
Streamline,
“There is a tendency to feel more comfortable with low V1”, whilst I heartily endorse being “GO minded” at higher speeds approaching V1, I feel uncomfortable when V1=Vmcg (as it often is). Test flying has shown me the
EXTREME directional control problems that can arise here, my mate
John_Tullamarine can provide some pretty graphic accounts of testing in this regard. I’m much more comfortable when V1 is a little above Vmcg. This is one area
seriously in need of a fix.
”one sees that people are inclined to use the wet RTOW in conditions that approach but are not quit like the wet scenario”. You’d better have a good lawyer, a very very good one. The law requires that for NORMAL operations, a screen height of 35 feet be achieved, and that one means of retardation be kept in reserve for the RTO calculation. Wet runway operations (when the AFM has clearly spelled out what constitutes a wet runway), allow for a legal
dispensation to use a 15 foot screen height and full credit for Reverse Thrust. In short there is NOTHING in reserve for the RTO, and a dramatically reduced screen height (and obstacle clearance height). Using this dispensation on a ‘less than AFM defined’ Wet runway is patently illegal. If you really like the lower V1s that go with the Wet Runway data for use on an ‘unwet’ runway, do two things –
Firstly, reduce the ASDA by 15%. That’s the reduction required by the FARs for an aircraft without a reserve means of retardation. It’s not in FAR 25, but in the FAR defining the requirements for aircraft certification (I’m on leave and don’t carry the FARs with me).
Second, calculate the 1st segment gradient, and subtend this gradient (typically about 0.8%) for the extra 20 feet screen height required back along the TODA to find the TODA reduction. That’s about a 2500 ft (762M) reduction for 0.8% gradient, worse for an Up-Sloping runway). With the new ASDA and TODA, go back to your Wet Runway charts to find the new MTOW, and you’re legal! Sorry
Mutt, another unbalanced field.
This ignores the effects of reduced acceleration and deceleration considered for the Wet runway, so this will be a small bonus if the runway is less than ‘legally wet’. If you use Contaminated Runway data, as
Marcellus Wallace has discussed, then the additional safety margin will be even greater.
Sorry if I’ve seemed to have hijacked the thread, colleagues, back to my leave now. I'll leave you in peace
Regards,
Old Smokey