Do you have a hard deck on a non-precision?

[Allan]

B737 question again Boeing recommends that you, when flying a non-precision approach using v/s, set the missed approach altitude 300' before reaching your MDA. Doesn't that present a problem with regards to protection yourself from busting your minium descent altitude? What do you do??

Kind regards

[Rainboe]

Where does it say that? I've always used either the 2500' Radio Height warning or the Outer Marker as a final place to check full flap, gear down and go-around altitude set. At 300' to MDA, you should really be concentrating on flying!

[Allan]

Flight Crew Training Manual, 5.58 "Approximately 300 feet above the MDA(H), select the missed approach altitude".

[Rainboe]

Does it actually say "set the missed approach altitude by 300' above the MDA"? That would make more sense.

[Flughaven]

With out ops we wait till ALT HOLD and then set Missed APP Alt and perform the G/A ........ Just for the reason you described.

[Pilot Pete]

It sounds like you are mixing two methods of flying a non-precision approach. If you are going to fly down to MDA and then fly level at MDA to the MAP, then you would put the MDA (rounded up to the nearest hundred) into the MCP ALT window.

If you are flying a constant decent rate non-precision approach where you have no intention of flying level at MDA (which is recommended in 'big jets' as it stops destabilising the approach late on whilst seeking visual reference and then attempting to re-establish descent to land), then you set the missed approach altitude after you level at your platform (in ALT CAP) and then commence descent at the appropriate point using V/S to your non-precision dicision altitude (my generic name for your 'revamped' MDA, which in our company is MDA + 50'), which is where you make your decision to continue or go-around, the 50' giving you the buffer for descent whilst initiating the go-around.

With the second method above it is no different to flying an ILS to DA, there is no auto-level off on that type of approach either, so no less safe in this respect IMHO.

PP

[willfly380]

allan that is the VDP method, is it your company policy to use it.it is definitely more safer way of doing a non precision approach. mda in this case defintely means minimums , it has to be properly planned and included in the company ops and training. you hit mda and either you land[if visual cues established] or you go around , no level segment in this method. the rest pete above has explained. but you must check your sops, this method if followed by your airline is very good and safe but results in more GAs as the ducking under is eleminated. and companies like flight safety as long as it doesnt cost them more that buying cassettes for cvrs etc.

[safetypee]

A source of confusion may be in the reason for the procedure on some versions of the 737 autopilot / FD and many similar systems in other aircraft. In order to leave a captured altitude the ALT SEL must be selected away from the existing altitude in the direction of intended flight. Thus for a non ILS approach (VS) the ALT SEL is set below the current aircraft altitude. There are hazards in setting MDA or even worse zero, thus the ALT SEL must be reset to the missed approach altitude, a check that this has been done at 500/300 above MDA is a realistic safety guard.

PP, while there are no ‘safety’ differences in the operation of the autos/FD, there are significantly differences in the type of approach; I think that this is what you meant.
NPAs are five times more hazardous than precision approaches (FSF ALAR Tool Kit), thus they should be briefed and flown as a non-normal procedure. Thus in this instance the operation of the autos/FD will be non-normal.

[duece19]

Pilot Pete

In my airline we fly Constant descent NPAs. However we do set MDA in the MCP window. Now if we level of with ALT ACQ and HOLD then its a Go around, even if you become visual when you just are entering the levelphase, if you do become visual before MDA then disconnect, reset mcp to missed approach alt and recycle flight directors.

It sure works fine, in the event of a go around, you level off for two seconds, set the missed app altitude and then go around.

Duece

[Tonic Please]

How do you "recylce" flight directors?

[Allan]

I do thank you all for your contributions to this discussion. We have not yet decided what to do. As I see it, you can't select one method that gives you no disadvantages. If you fly a CDFA which is generally recommended, you cannot tolerate a level-off at MDA because your profile will be "comprimised". This means that your altitude selector cannot be set to your MDA when you reach it. This further means that you have no protection from going below your MDA and, in the worst case scenario, no protection from CFIT because you will get NO warning from the GPWS since you are fully configured, and you CANNOT be certain that the profile you have established, both horisontally and vertically will deliver your aircraft on the runway, even if you are established, e.g. NDB approach+- 5 degrees. On the other hand, if flying a "dive and drive" approach with altitude selector at MDA, you will probably have a higher workload with controlling v/s and airspeed and roll issues if on single engine, also an increased workload if capturing altitude at MDA, increasing thrust, setting missed approach altitude and so on...... But again, please continue this discussion, why invent something myself when I can stand on the shoulders of geniuses.

Kind regards

[safetypee]

Allan, you present a very logical argument, the balance of which could be changed with the advent of EGPWS, now mandatory in large commercial aircraft. The new system will warn if the aircraft is flying an incorrect profile (vertical & lateral) even when fully configured, and will detect obstacles if the appropriate data base is loaded and updated. However I am not advocating reliance on EGPWS, it is the final safety system for situations where either you or someone else makes a mistake.
The obstacle free zones in NPA procedures provide sufficient margins of safety provided the approach is flown accurately, thus your concerns could be reduced by lowering the pilot workload - concentrate on rule #1 – fly the aircraft. Also the professional pilot is taught the importance of discipline, i.e. not descending below MDA until the visual references are seen. This requires a good instrument scan that is essential for accurate flying; this includes altitude awareness and the margin above MDA. You also require good knowledge of what the visual cues should be for the decision to continue below MDA (head up).

There are many arguments against flying level (dive and drive), not to be repeated here; however for a continuous decent there is the bonus of having the aircraft on a known ‘stable’ flight path on which to judge the continuing, predominantly ‘visual’ flight path towards the runway, as opposed to the unstable level off / recommence descent flight path; back to rule #1 and the simpler lower workload option.

Tonic “How do you "recycle" flight directors?” Most flight guidance systems will reset to the basic modes (e.g. pitch/roll) if the FD is switched off and then on; this is recycling. Be aware that in most aircraft both FD displays have to be set off / on again; however his procedure can be distracting, involve higher workload, and be subject to error, thus should not be considered as part of a procedure at low altitude. If the flight guidance is inappropriate then switch it off and fly the basic instruments – rule #1.

duece19, what happens if you go around below MDA, after a land call – baulked landing etc. Does the FD acquire the MDA altitude giving a fly up indication while you descend, do the crew ‘remember’ to select GA mode, what altitude is the GA flown to, and what safe guards are there for capturing that altitude? ‘Your’ procedure appears to have weaknesses, high workload and opportunity for error in unusual circumstances; all ingredients of an incident.

[duece19]

safetypee

Erm, let me see where to start.

When you recycle the flightdirectors on 737NG as I fly, they arm and are available but dont show anything because you have no modes selected. Therefore they are available below mda and when you do go around, you press your TOGA buttons and here we have track and GA (a speed reference system) on you flight directors, now that guides you up towards mda if thats what you mean. For the workload bit, it takes approximatly 1.5 seconds to recycle and twist in the published missed approach altitude on the plate, the workload is not a factor here. Now after that you'll select LNAV and autopilot whom will then fly you automatically on your missed approach track and up towards your missed approach altitude while cleaning up the airplane.

And yes, crews do remeber to select GA modes, if one forgetts the other one is there, and I dont see how our procedure would be dangerous because of that. Now Im not saying its the best available, but it sure works fine, and what it does, most importantly is prevents us from descending below MDA.

With this procedure we never level off and then continue and NPA, if we get to level off without rwy in sight, then its considered to be too poor wx. That is kind of safe is it not? Even if we fly level for 10 sec, we still wont have reach the MAPt already be on our way up in the sky.

Dont know if thats what your concerns were but, just approach me again, and if there is some better ideas im happy to hear them.

Duece

[safetypee]

Thanks for the clarification Duece, my knowledge of current flight guidance systems is becoming dated with the advent of NG etc. However if the FD is in GA below MDA, which is set in the ALT SEL, will the FD capture that altitude, or is this dependant on the crew resetting the ALT SEL to a higher altitude before a GA? Thus at or below MDA the FD is ‘recycled and the ALT SEL reset; who selects, who flies, who monitors?
I would still maintain that workload is higher than necessary; could some of the operations in ‘your’ procedure be sequenced earlier? If so then workload and opportunity for error can be reduced. i.e. in the event of a GA, in addition to recycling and resetting, who is flying, who is reconfiguring, who is monitoring? Surely something might be missed in those critical first few seconds of a GA.


I am not seeking to be pedantic nor suggest that ‘your’ procedure is unsafe, but many arguments similar to those you make are often seen in accident reports - “workload is not a factor here”, or “crews do remember to select GA modes, if one forgets the other one is there”. All the industry seeks is to improve safety by reducing the opportunity for error.

“… if we get to level off without rwy in sight, then its considered to be too poor wx. That is kind of safe is it not?”
It is as long as crews are disciplined and are not tempted to continue the approach … and that never happens? The alternative procedure that uses a continuous decent to MDA (+) and then GA immediately if the required visual cues are not seen, has one less error path, which could be argued as being ‘safer’, but safety involves the balance of risk and risks are balanced by humans and humans make mistakes.
As part of the successful FSF ALAR Tool Kit I understood that all of the major manufacturers were to encourage a stable continuous descent with GA at or above MDA, however it appears that the Boeing procedure for ALT SEL setting is open to a wider interpretation than others.

[Pilot Pete]

safetypee

PP, while there are no ‘safety’ differences in the operation of the autos/FD, there are significantly differences in the type of approach; I think that this is what you meant.

You indeed interpret my comments correctly.....obviously NPAs are significantly less inherently safe than precision approaches.

duece19

Thanks for the insight into your method of flying NPAs. It just shows how many ways there are to skin this cat! I can see fors and againsts for both methods......

PP

[alexban]

Safetypee:..The procedure deuce described is like this: FD off,set missed app alt on mcp,then FD on (you can set only PNF FD on -recommended by Boeing) .So ,in case of go-around bellow MDA you'll climb to the missed app alt.
We use both procedures,depending on the particular approach.Most common ,we use the step down procedure.
If you configure the plane before FAF then you'll have no problem with the speed during step descent.It's easy to follow ,using the green arc,easy to monitor-callouts-ALT ACQUIRE,ALT HOLD,SELECT NEXT ALT.
At MDA you'll be level,should select missed app alt on the mcp and check arrival at the visual descent point.HERE you should decide to land or go-around.
One important thing often overlooked,the visual descent point V it's not necessarily the same with the MAP.Sometimes the MAP can be after the end of the RWY.If you do a CD app how will you manage that?
Also ,I guess the risk for going bellow MDA can be higher with the CD app in cases where stress ,for ex,could result in a failure to announce arrival at the MDA (stormy weather,or malfunctions...) .In this case you are set for a CFIT.
If you do a step down ,the plane will level at the MDA,even if you forget to call approaching MDA.
And don't take for granted the EGPWS,maybe the database it's out of date.It happened before.
Both procedures are ok,but should be carefully briefed and be apropriate with the arrival .

Brgds
Alex

[safetypee]

Alex, I fear that your procedures are moving back to the problems and hazards of step down / dive and drive procedures. I thought that the industry had learnt these lessons several years ago and even ICAO had suggested that CDs should be mandated. The worldwide safety initiatives CAST and JSSI have also made recommendations; JAA have proposed a change to JAR-OPS1 ‘ OPS-20 (Stabilised Approach)’; I cannot find the reference on the JAA web pages thus it may now be in JAR-OPS1.

From the proposed amendment: Another reason for reviewing the requirements for instrument approaches is the CFIT and ALAR programmes (JSSI), which encourages the authorities to prescribe stabilised instrument approaches as a means of reducing the non-precision approach accidents. The elimination of Non Precision Approaches (NPA) with level flight at Minimum Descent Altitude (MDA) close to the ground and avoiding the change of attitude and power/thrust close to the runway is seen as a way to reduce operational risks.

JAR-OPS 1.430 (d). A requirement for stabilised approach has been developed … . In those cases where the stabilized approach concept cannot be applied, it is required to apply the add-on to the RVR. The requirement to fly stabilised approaches is proposed to become effective immediately.

JAR-OPS 1.430 (e). A more developed variant of the stabilised approach is the continuous descent final approach concept (CDFA). In addition to flying stabilised on the approach there are also other requirements such as vertical guidance or simple methods of controlling the descent, the length of the final approach segment, etc. This concept also aims at improving the safety of non-precision approaches. The draft also contains a proposal to give the operators and aerodromes three years to prepare for the full application of CDFA since the preparations will typically include revisions to the Operations Manuals and training and will most likely also affect the provision of facilities for instrument approaches (including GNSS based approaches).

Para (b)(2). The use of the MDH as a DH is a consequence of the method of not allowing level flight at MDH (or multiple step-downs during non-precision approaches). This method is widely used among major European, commercial operators and more than half of those operators do not apply an add-on to the DH. It was however felt to be prudent to remind the recipients of this NPA that the application of MDH as a DH is a matter, which needs to be evaluated and which may need to be discussed between the operator and his Authority.

As you realise the MAP has nothing to do with a CD, or with achieving a successful landing. The VDP is the optimum position for transferring to a visual approach and must be at or above MDA. The skill in flying a CD in non VNAV aircraft starts with the assessment of GS and required VS, then accurate flying – a stabilised approach.

“And don't take for granted the EGPWS, maybe the database it's out of date. It happened before.”
This is entirely the operator’s responsibility; the databases can be updated on-line here: EGPWS, this also includes the obstacle databases which can be incorporated by local or manufacturer’s modification, and a listing of all airports covered

A safeguard against missing the MDA (two crew, bugged alt?) is to remember that no NPA has an MDA with less than 250 ft obstacle / terrain clearance, thus use the Rad Alt, if you see 250 ft and are not visual then GA.

[OzExpat]

if you see 250 ft and are not visual then GA

That will work if the controlling obstacle is right at the point where you observe the Radalt.

[alexban]

safetypee: i guess you are right,one question though:
in case the MAP is at threshold or even beyound the rwy,if you do a CD what will you do if you won't see the rwy at MDA?
Go around there or fly level at the MDA to the MAP ,then go-around?I thought that the second is right,but maybe I'm wrong. confused: If this is the case wouldn't be better if you have the mda selected on the mcp?
Also,what are the risks in the step down,if you are full configured at the FAF?
The VS won't be higher than 800'/min,so no problem with the speed.I did it this way for years now,no problem with the mda or speed ,or whatever during descent.
Of course ,some may find dificult to control the plane with the change in attitude and thrust during level flight,but such a pilot could also miss a check and fly nicely into the ground.
And stress could be a big issue,such as to cause a MDA call miss.I've seen a Flight Safety material,with a particular flight,very bad weather,where the GPWS 'to low','pull up" has sounded for almost 30 sec,and both pilots didn't even remember hearing that.They've been extremly lucky,i may say.

" The step down descent is a traditional method which involve changing the flight path at low alt and is not similar to the ILS (hence the increase risk).This method often require of the crew a higher level of skill,judgement and training than the typical ILS app." --Boeing 737 FCTM.
So,lack of training should be the main reason for the increased risk. I guess you are right.
Brgds Alex

[safetypee]

Alex, “MAP beyond VDP”: the procedure design requires that the lateral flight path is followed accurately, so the aircraft must over fly the MAP and follow any turns or track constraints of the missed approach procedure. The vertical profile is not restricted, except as published, which is normally to climb to the missed approach altitude, thus the GA climb should be commenced immediately at MDA or at any time if uncertain of position; call ATC and climb to MSA.

“Hazards of a step down approach”
Descending too early:-
A320 Aalborg Denmark, used incorrect DME for descent point, saved by EGPWS.
B737 Cordova Alaska, FMS failure, EGPWS save
B727 Pointe-a-Pitre Guadeloupe, sink rate warning at 150 ft at 4.5 nm
HS748 Isle of Man (2 events)
F28 Sylhet Bangladesh,
B747 Guam, fatal
B747 Lagos Nigeria, incorrect DME
A310 Dhaka Bangladesh, VOR/DME 170 ft at 4nm
B747 Madril Spain, Mis-set ALT SEL
B737 Tegucialpa Honduras, descended at 10 nm instead of 7 nm
Several mistakes with FMS programming, incorrect DME, misleading or mis-reading charts.

Steeper descent than profile – missing a step altitude (some accidents above MDA):-
BAC1-11 Tamanrasset Algeria, VOR/DME fatal
J31 Hibbing USA, fatal
A320 Strasbourg France, fatal
B737 Mokop Korea, VOR/DME fatal
A310 Katmandu Nepal, NDB, VOR/DME fatal
Some procedures have descent rates less than 800 ft/min, there were some less than 600 ft/min

Descent below MDA:-
A320 Gatwick, GPWS save
RJ100 Zurich, false visual, fatal
B737 Salta Argentina, EGPWS save
B737 Brazil, distracted by cargo smoke warning
RJ100 Dyerbakir Turkey, VOR/DME, false visual in fog, fatal

Thanks to Honeywell (Don Bateman, Yasuo Ishihara, and Steve C. Johnson) for the data from a limited distribution publication “Flight Into Terrain II”, but now available on request here.

EGPWS is more attention getting with audio and visual ‘popup’ terrain displays; info here Just How Effective is EGPWS?
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Airspeed and Upwardness