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Boeing 737NG VREF ICE - only for flaps 15?

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Boeing 737NG VREF ICE - only for flaps 15?

Old 5th Nov 2011, 20:22
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Boeing 737NG VREF ICE - only for flaps 15?

Non-Normal Checklists, when we have problems with high lift devices and :
- engine anti-ice will be used during landing
- wing anti-ice has been used any time during the flight or
- icing condiions were encountered during the flight and the landing temperature is below 10 degrees Celsius
require to use VREF ICE = VREF 15 + 10.

I wonder if we use flap setting another than 15 and above conditions shall we use ICE additive to VREF?

Thanks in advance
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Old 6th Nov 2011, 16:56
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The Part B Procedures 2.35.2.15 says -700: Use normal procedures and reference speeds unless a Flap 15 landing is planned. So it is not just in the event of a leading edge device problem that you may use Vref ICE. For example, all 737 one engine out landings are made with Flap 15. The best way to do this is on the FMS Approach page when you select the Flap 15 approach speed, simply amend the line to read 15/(approach speed +10).
The NG Vref ICE differs from the Classic 737 and Vref ICE is used for any Flap 15 landings ONLY, no others.
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Old 6th Nov 2011, 18:06
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To Notso Fantastic

Thank you for answer.
But I am interesting to know - why?
May be NG VREF 15 is more close to stall, than VREF for other flap setting?
For example, in case of LE FLAPS TRANSIT on the Classic 737 we should set VREF15+5
but on the 737-800 we should set VREF15+15 (10 knots more)
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Old 6th Nov 2011, 18:44
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For example, all 737 one engine out landings are made with Flap 15
Not true. The one engine inoperative landing checklist has a decision tree at the beginning which says:

1 Choose one:
  • Landung using flaps 30 (if performance allows): Use flaps 30 and Vref 30 for landing and flaps 15 for go-around. Go to step 4.
  • Landing using flaps 15: Go to step 2.

Step 2 then points to Vref 15 or Vref ICE which is Vref 15+10, step 4 just continoues with the normal flow at Use engine anti-ice on the operating engine only. Of course a note within the flaps 15 part of the checklist advises that autoland is not authorized.
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Old 7th Nov 2011, 13:51
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Im checking NG QRH now,

One Engine inoperative landing

Condition: Landing must be made with one engine inoperative

1- Plan a flaps 15 landing
2- Set Vref15 or Vref ICE
If any of the following conditions apply, set
VREF ICE = VREF 15 + 10 kts

-Engine anti-ice will be used durind landing
-Wing anti-ice has been used any time during the flight
-Ice conditions were encountered during the flight and the landing
temperature is below 10c.

I dont know others 737, but we land with FLAPS 15 with an engine out landing for sure.

I think this is because the sweep angle, it is not the same as others 737. Perhaps the wings work differently than the old 737 with a thin film of ice.

I hope it helps!
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Old 7th Nov 2011, 14:25
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Its about maneuvring margin at flaps 15 with possible ice accretion on slats,stabilizer....
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Old 7th Nov 2011, 14:44
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From a previous post of this subject,, not by me but nevertheless.ps..apologies for the paraphrasing!

e. The reason given why Vref Ice is applied to the NG and not to the Classics is that they have different wings. The Vref Ice policy was because when Boeing was doing initial flight testing, they put artificial ice on the wings. The FMC automatically compensates for the change in performance for the ice at flaps 30 and 40, but was not sufficient to compensate for flap 15, so an extra 10 knots has to be added for performance, and to keep the Ref speed out of the amber band.

The problem with the ice was not the wings but the empennage.
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Old 7th Nov 2011, 15:52
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@M.82, i was talking about the NG as well, the classic cannot do flaps 30 OEI landings and no autoland with OEI either. Our older NGs have the same checklist you posted, our newer ones have the decision tree i mentioned. Not quite unimportant as the OEI flaps 30 landing allows a CAT IIIa approach and we do not need any take off alternate usually.

And in the same checklist under the same condition only flaps 15 need the VREF ICE of course, flaps 30 doesn't.
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Old 7th Nov 2011, 16:34
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Is it not because the outer slats are not de-iced/anti-iced so it is to allow for greater margin if there is ice build up here?
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Old 7th Nov 2011, 19:12
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Avenger, do you have a link for the quote in #7.
Not that I have any evidence that the statement is incorrect, but as stated it does not appear to be consistent with either aerodynamics or certification principles.

Speed additives are normally associated with lift / control margin, where the wing is a dominant factor.
In addition the NG may have been subject to revised certification for flight in icing; there were also changes to autoflight approval in icing conditions.
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Old 7th Nov 2011, 20:07
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Denti

Are your NG's fail-operational or fail-passive?
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Old 7th Nov 2011, 22:09
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"The FMC automatically compensates for the change in performance for the ice at flaps 30 and 40,...."

Please explain how this happens.
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Old 8th Nov 2011, 04:36
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Apparently some operators use a more clever FMC version 10.X
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Old 8th Nov 2011, 10:22
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The quote came from a debate on this forum in 2007, which again appeared in 2009.. There was some reasoned arguements at the time.. I'm not going to re-invent the wheel.. http://www.pprune.org/tech-log/379404-737-vref-ice.html
I think the ref to the FMC compensating for ice in " normal landing configurations" is confusing, perhaps they should have simply said the margins are greater than in Flap 15 landing config..
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Old 23rd Mar 2019, 04:16
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But not the leading edge flap transit non normal!!

thats what Id like to know! Directs to F-15 approach and landing but no vref ice in that check list!
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Old 23rd Mar 2019, 12:26
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The FMC will adjust stick shaker and the min maneuvering speed bar when the wing anti-ice switch is selected on, and it will keep those adjustments for the remainder of the flight regardless of the switch position.

It will not adjust any Vref.
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Old 23rd Mar 2019, 15:22
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The B737 Classic Supplementary Procedures Adverse Weather in the Operations manual states add 10 Knots to VREF if ice formations are observed on the airplane surfaces. A Note states "To prevent increased landing distance due to high airspeed, bleed off the airspeed in excess of VREF + 5 knots+gust correction when below 200 feet AGL. Maintain the gust correction to touchdown.

Disregarding the ice additive for the moment, this brings up an interesting question. The 737 Classic FCTM under Landing Airspeed Control says "..maintain VREF plus the wind additive until approaching the flare." The steady headwind additive is bled off before touchdown while the gust correction is maintained to touchdown.

During a manually flown approach (no icing) where the steady headwind component is high - say 30 knots, so that half the steady HW component is 15 knots, then somewhere on short final steps must be taken to start reducing the airspeed as recommended. From personal observation many pilots hang on to the half the HW component until the flare despite the FCTM advice to bleed off that additive until approaching the flare. This generally results in excessive airspeed which is a no no..
The term "approaching" the flare is therefore rather vague and open to different pilot opinion.

A clue to the Boeing intent ("until approaching the flare") could be the instruction re ice additive of 10 knots to VREF plus the other wind additives where the Supplementary Procedures states: Bleed off the airspeed in excess of VREF + 5 knots+gust correction when below 200 feet AGL.

In other words start the reduction at 200 feet AGL,of half the steady HW. Not wait until the flare itself.
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Old 23rd Mar 2019, 23:33
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Originally Posted by M.82 View Post
Im checking NG QRH now,

One Engine inoperative landing

Condition: Landing must be made with one engine inoperative

1- Plan a flaps 15 landing
2- Set Vref15 or Vref ICE
If any of the following conditions apply, set
VREF ICE = VREF 15 + 10 kts

-Engine anti-ice will be used durind landing
-Wing anti-ice has been used any time during the flight
-Ice conditions were encountered during the flight and the landing
temperature is below 10c.

I dont know others 737, but we land with FLAPS 15 with an engine out landing for sure.

I think this is because the sweep angle, it is not the same as others 737. Perhaps the wings work differently than the old 737 with a thin film of ice.

I hope it helps!
The QRH for Fail Passive aircraft only offers a single engine flap 15 landing. On Fail Operational aircraft the option is offered for a single engine flap 30 approach as the aircraft is approved for a single engine flap 30 approach to CAT 3A minima
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