HUD as PFD

[juliet]

Hi all,

I posed this question a while ago on a thread about the A380 but didnt get much in the way of an answer, so here goes another try!

Why is only 1 HUD used when installed in modern aircraft? It seems that aircraft with a HUD, ie. big business jets, A380 etc, only install 1 HUD, and apparently not as a PFD.

From what I have seen the HUD is generally only used as an aid in addition to the heads down PFD. As such the heads down screen is still used to display PFD info. If the HUD were used as the PFD then that heads down screen would be available for nav info, radar, moving map, whatever.

Further to this there is generally only 1 HUD installed. The Captain is able to look outside but the Co is still heads in and looking down.

It seems that in current use the HUD is seen only as a temporary aid for the approach phase of flight, and not really used at other times.

I have experience on a multi crew flight deck with 2 HUD setup certified as PFD. It is fantastic to have both pilots looking out the window and to have the screen directly in front of the pilot available for nav info.

If anyone has an idea as to why HUDs are used in their current manner I would like to hear about it, as from my point of view most HUDs are not being used to their full potential.

Cheers

[Gerz]

C-130J has Hud certified as a PFD. Can't recall if it has two however.

Problem with HUD PFD is that it tends to get cluttered....

[juliet]

Hi Gerz,

C-130J does have 2 HUDs, both for use during the entire flight envelope. They are set up very well in that they free up a whole head down display for the nav/radar display.

Interested in what you say about a HUD being cluttered if used as a PFD. This certainly isnt the case on the C-130J. In fact it has far more info displayed than any civ aircraft would require, in terms of mostly tac timing displays. The HUDs are large, clear, and provide a lot of info without taking away from the view out the front.

Are you flying with a HUD? Only have HUD experience on 1 type so would be keen to hear what others have to say, particularly what info is displayed.

Cheers

[Nigd3]

Juliet

It may be something to do with the criticality of the system from the certifcation point of view and it meeting all the relevant DO-178B, DO-254 and DO-160 quals.
On top of that it would also struggle to meet the FAR requirements for use of colour for warnings, cautions and advisories for the various flight information (speeds etc) if certified for use as the PFD.

This is a "off the top of my head " type of answer but maybe something to investigate further.

[Northbeach]

I believe the Boeing 787 Dreamliner will be produced with each pilot having their own HUD. I fly a NG 737 with the HUD and like it most of the time. But there are two drawbacks with the arrangement. First is its potential to mask traffic. This is a problem every time I fly in congested terminal airspace. Often I move the HUD up and out of the way under those conditions. The second is the transition from flying to landing and then turning off the runway. By design the HUD clears some information, but what remains is a distraction once you clear the runway under many visibility conditions. You have to drop your eyes down to locate the shut off switch or ask your flying partner to turn it off who then has to drop their outside scan to locate the switch. Boeing should have put a HUD turn off/on switch on the yoke or the tiller.

[Nigd3]

Northbeach

Some valid & interesting points.
An aircraft manufacturer may come up against opposition from the certifying authority if it attempted to have an on/off switch for something that is certified as the PFD, however as I don't know if this approach has ever been tried, it is speculation from my side.

Another point with the HUD is that it is actually taking the pilots view away from the optimum primary field of view, when taking into account an instrument panel scan as a whole, with minimum head/eye movement.

[juliet]

Nigd3,

Full colour HUDs are available, thereby replicating a head down PFD in that respect. In terms of criticality, I take it you are talking about what happens if the HUD fails? Pretty standard for a HUD failure to cause a PFD to come up on the appropriate HDD so that you just end up in a 'normal' situation. As I said HUDs have been certified as a PFD so I imagine these problems have been addressed.

Northbeach,

I know what you mean with regard to HUD masking and as an annoyance on the ground. I found that in the air it just takes small movements of the head to effectively "look behind" the HUD symbology. On the ground it is usual to just push the HUD forward. This effectively turns the HUD off, brings up a PFD on the HDD, and allows a clear view forward. The normal stowed position of the HUD is found by pulling the HUD towards you, causing it to rotate upwards and finish flush with the ceiling of the cockpit. I am guessing that the HUD you use doesnt move? Obviously different equipment will need different techniques, so what works on one wont on another.

As an aside there are a few other problems with using a HUD, as Northbeach points out. Very bright lights on approach can cause parts of the HUD to become difficult to view for example.

I think that with some of the technology out there the HUD is going to become pretty commonplace. The G550 for example already uses a HUD to display imagery from a forward mounted camera for low vis ops. As such it is going to be in effect the PFD, so why isnt this taken into account? Just seems like a waste to have all the PFD info duplicated.

[Flaperon777]

Ever heard of a "paperless cockpit"...?? One pilot still has to have hard copies of EVERYTHING.Well,at least during certification that is....(which may be anything from 6 months to 36 months incidentally!)
Having instructed a few thousand hours on a dual HUD mid jet(with certification for single HUD use only at any time by the way),all I can say is......same principle applies! The certification authorities just are'nt comfortable with dual "non redundant" systems being used during 'critical phases' of flight.
Think about that.......:rolleyes:

[juliet]

The certification authorities just are'nt comfortable with dual "non redundant" systems being used during 'critical phases' of flight.

Hey Flaperon,

Can you explain that one for me?

Cheers

[Cyclone733]

I'd imagine the driving force is still cost.

HUDs are an optional extra on the type I fly, for the Captain only, primarily used on the approach to reduce the limits on visibility and DA.

If the units have a limited life of operation due to bulbs/burn in or similar it makes sense that they would be used only in the descent and approach phase of the flight. As such their use as a PFD wouldn't make sense as the pilot would have to learn 2 different scans. One using head down instruments and one using a combination of the HUD as a PFD and the other displays in an unusual display mode.

Even if the HUD were used as a PFD would a HUD failure ground the aircraft? The thinking being that you've lost a primary system and are relying on a backup (even if you are back to using what everyone else is) Not sure if you could class it as a deferable defect

The units available on the type I operate are steam driven monochromo and appear to have a relatively low resolution, so I wouldn't see them being very useful in displaying all of the information from the PFDs in a clear manner.

As the technology improves and filters down from military applications I'm sure the reliability will increase and the cost fall at which point we'll see HUDs becoming more common place on both sides of the cockpit and for a larger range of uses.

[Northbeach]

Juliet,

I hadn’t thought about pushing the HUD forward out of the way. I will look at that option the next time I fly thank you for the tip.
While I’m rolling out, decelerating and looking at the next taxiway I am really not too thrilled about having to move one or both hands off the throttle/yoke/tiller to do battle with the HUD as retracting it to the normal stowed position is a two handed affair. Boeing already has a “clear” button; they should have put a repeater button on the yoke or tiller.

[Nigd3]

I think Cyclone773 has the most probable reason.

HUDs are still relatively new to the civil world and are not being forced by any legislation (as TCAS and EGPWS etc were).

I have to admit, I need to come up to date with HUDs and their current capabilities.

[juliet]

Northbeach,

I think you are right about a button on the control column to turn the HUD off. Having to take your hands off the controls to move the HUD isnt ideal, but I guess I am used to doing it. I think your idea makes more sense, and it would be easy to have a button for it. On my type there is already a button on the yoke that brings up a PFD on the HDD, though this doesnt turn the HUD off.

Cyclone,

I think you are probably right re cost. Its cheapest to not have a HUD, next cheapest is 1 HUD, 2 HUD most expensive.

As for different scans, surely if you are only using the HUD for the approach you are having to use a different scan all the time? Wouldnt it be better to only use the HUD and therefore the 1 scan?

On my type a HUD failure doesnt ground the aircraft. 1 failure means the other pilot flies with their HUD while the pilot with the failed HUD goes back to the old HDD PFD. Both HUDs failing just means both pilots use their HDD PFD like they would in a normal aircraft.

Interesting what you say re ideas coming down from the military, this has typically been the way things have happened. With regard to the use of a HUD I think this is still the case, but in terms of technology I think it is the civ manufacturers that are leading the way, with Gulfstream and its EVS being a prime example. They are doing stuff now that is really advancing aviation at a fast rate. Allowing a DH to be reduced using internal visual aids is pretty impressive.

Cheers for the replies so far guys. Interested to hear from any of the guys flying with EVS if possible?

[Cyclone733]

Juliet,

As far as the differing scans are concerned, in the setup on my aircraft's HUD system, the HUD only provides basic information and not a full PFD representation. So in the case of looking away from the HUD for whatever reason the main displays are still PFD, MFD and ED where as if the HUD was providing PFD information the normal PFD screen may have a Map display the MFD a weather radar or other data displayed changing the normal scan.

Which in itself isn't an issue unless the particular aircraft you were operating
has a U/S HUD system or you were to only use the HUD as a foul weather approach aid in PFD mode with a different HDD setup. Which on re-reading the earlier comments isn't the direction this thread was heading in.

I'd be interested in knowing the design process with the HUD interface. Is it driven purely by engineers or are flight deck actively involved in the process? An engineers view of the way the system will be used and the pilots can be very different as another thread is alluding to.

Interesting to note it is a field being driven by the Biz Jet side of the market where getting into smaller less well equiped fields (ie no CatIII etc) appears to be the driving force and I'd imagine a great selling point. "Yes our aircraft is $1mil more, but our aircraft will get you to your chosen destination and not a diversion airfield, more of the time than our rivals"

[juliet]

Hi Cyclone,

Yeah I think we are drifting slightly but hey, thats the joy of Prune!

I think what you are saying is that where the HUD is the PFD, and the head down displays normally do not show any PFD info, the loss of the HUD would mean an unusual head down set up?

This situation on my old type leads to a PFD in front of the pilot instead of the normal nav/radar screen. Normally in this case the moving map display would be swapped for a nav/radar display for that pilot, so that they stay fully in the loop. The 4 screens would now be configured as (left to right) a PFD, a nav/radar, engine info, nav/radar (assuming a failure of the Captains HUD). Bear in mind of course that in this situation the pilot that loses his HUD would hand control to the other pilot so that they continue flying using the HUD. Preference is always for a pilot to be on the HUD rather than a HDD PFD.

Your last point is, I think, bang on the money!

Quite interested by this as my HUD experience seems to be in a totally different fashion to most others.

[Nigd3]

Cyclone

For displays in general there is pilot involvement all the way through from the equipment manufacturer, aircraft OEM and the certifying authorities.

Sometimes what the pilots would like is not financially possible, implementable or even certifiable.
Sometimes what the engineers would like is financially possible, implementable or even certifiable.
If you designed a display to the exact letter of the FAR requirements, that are sometime 20 years old, but hence certifiable, you end up with a system that both engineers and pilots dislike.

Engineers define the standard things like contrast ratios, panel/display luminance, symbology (in accordance with guidance material), formats, functions, tactile feedback and moding etc.
The pilots and cert authorities should by involved from the beginning to help ensure that the end result is operationally acceptable but also certifiable.

It ends up with compromises from all sides, which is one of the reasons why certain systems have "quirks" in them that as end user operators you maybe cannot quite understand why. They are quite possibly in there to satisfy a FAR requirement but operationally not that great.

The extract below is from a certification presentation I have and may go some way to explain what I have said above

FIRST LAW of certification:
REGULATIONS AND PROCEDURES ARE SET TO AVOID PERSONAL
INTERPRETATIONS

SECOND LAW of certification:
VERIFICATION OF COMPLIANCE IS ESTABLISHED VERSUS APPLICABLE & SPECIFIC REQUIREMENTS AND PROCEDURES. Any other interpretation is pure
SPECULATION

PS apologies for digressing, this is aimed at Cyclones question about the design process

[fm013]

The reason for single HUD installs only is purely one of cost. But as the purchase and through life cost of HUDs are coming down through the introduction of new technology, we are beginning to see dual installs. This in itself opens up some new operational and certification issues that will take time to get right.

There are colour HUDs, but not in the civil market yet. Colour HUDs developed for military platforms may be subject to export restrictions (e.g. ITAR) so it's not just a simple case of putting them in a commercial aircraft.

I'm not aware of any civil HUD certified as a PFD (unlike in some mil transport aircraft). But this will change as manufacturers push to free up head down real estate for other functions. The extra integrity (10e-9) and cert requirements for HUD as PFD also pushed up the cost so why pay the extra when you've already got a certified head down PFD?

HUD as PFD has a number of advantages over head down PFD. It can display the same primary flight info (speed and altitude tapes, HSI, pitch ladder, vertical speed, ...) but has the added advantage of being conformal and much larger field of view. On the HUD you fly the flight path vector, in the HDD you fly by attitude.

HUD users would love an on/off switch on the yoke but (at least from the 737NG point of view) Boeing won't have it. If users want it, they need to pressure on the airframer to let them have it. It's not really a big deal from a design point of view.

You can push the HUD combiner forward (at least in the NG) but this isn't its recommended stow position - it's the breakaway position to comply with head impact criteria. I'm not sure but repeatedly doing this (and not the proper stow method) may put the combiner out of alignment and therefore no longer be conformal.

EVS is becoming a major driver for HUD installs, initially on bizjets (e.g. G4 and 5) but now even Boeing and Airbus seem to be interested. You can use it to get landing credit down to 100 feet on a CAT 1 or NPA - i.e. CAT 2 minimums. So there is a good business case here.

[HiFli]

Northbeach, I've been away for awhile and now catching up on the forums. No doubt that by now you've discovered the little "trick" to stowing the HUD if you use the breakaway feature? Can be embarassing the first time round.

[MrHUD]

I was just perusing the net for details on HUDs and HGS and stumbled into this place. Cool site!

I work for Rockwell Collins Head Up Guidance Systems (formerly Flight Dynamics) for about 10 years now. And, accordingly, am painfully aware of the desire for pilots to have Dual HUDs and the resistence from the Finance departments to authorize double the cost.

So, the clear switch on the yoke. We fielded that question recently through Boeing. Might be same source as here, but it is going to be on the 787 yoke. Retro anything on the 737 is terribly expensive, but it's being examined.

As far as damaging the HUD alignment by pushing forward to the breakaway too frequently, probably not. But, it is a mechanical device and they can wear out.

The Dual HUD is clearly the way to go for so many reasons, and many of you are probably aware that Jet Blue has dual HUD Embraer aircraft. I believe that they are working toward dispatch reliability improvements by gaining approval for HUD as PFD. I'm not directly involved in that program, but if anyone wants to know I can certainly find out.

Feel free to email me directly about anything HUD, as we love to support you!

And remember, HGS - The best approach in any category.:D