NDB Approaches with ONLY ONE Receiver

[BEASTPLOTINTHEWORD]

Is it allowed to fly an NDB approach with only one receiver on board? (no FMS, nothing else)

There is no flag should the signal fail, and that's why we have to monitor the audio ident continuously, but still, the doubt remains.

Mind you, we have various airplanes with only one receiver installed...

[Keygrip]

Is it allowed to fly an ILS with only one receiver onboard?
Is it allowed to fly a VOR approach with only one receiver onboard?
Is it allowed to fly a GPS aproach with only one receiver onboard?

Is it allowed to fly an SRA with only one transceiver onboard?

Is it a good idea? Ah, now that's a different question.

[OzExpat]

It might depend on what your national regulations say but, for all the countries I've flown in (quite a few), it's certainly legal. But, as Keygrip has implied, you'd need yer head read to do it!

[Graybeard]

Legality of a single ADF approach depends on the category of airplane in the US. What kind and age of airplanes are you flying?

The US Air Force bought a bunch of 737-200 in the 1970s as training aircraft, and called them T-43A. They bought them with only a single analog-tuned ADF, as they were never expected to make serious ADF approaches.

As these things go, of course, the planes were pressed into VIP service. The USAF always had millions for new, glitzy projects, but pennies for valuable upgrades, so the T-43A never got the second ADF, let alone GPS, which was widely available to them by 1994.

That's when a T-43A based at Ramstein flew to Bosnia one stormy night with the US Secretary of Commerce and other VIPs. Their ADF approach required crossing one NDB, then tuning to another near the field. The pilots failed to correct for crosswind on the outbound leg and impacted terrain...

The analog-tuned ADF receiver was superseded by a digitally tuned analog receiver in the mid-1970s. The analog-tuned unit at least had a nervous needle, which signaled the pilot it was working, unlike the later unit with its well-damped, seemingly dead needle.

GB

[212man]

I thought the point was that approach required two ADFs to be tuned to two separate NDBs simultaneously (in line), to ensure accurate tracking, and that was the problem: they only had one ADF!

[Basil]

two separate NDBs simultaneously (in line)
Only possible in the event that there are two separate MF beacons in line with the approach; not always the case.

When I started flying I predicted that by the time I retired both NDB and HF would, like the three pointer altimeter, be obsolete; regrettably I was wrong.

On some older installations pilots at least had a large prominent radio compass or RMI and were in regular NDB approach practice. Unfortunately, later installations buried a tiny RMI with no QDM bug in a corner of the instrument panel where it is more difficult to scan and, in any case, the pilots rarely get the practice of flying a genuine NDB approach.

Used to operate into a grass strip where the guys built their own MF transmitter and used crosscuts on a nearby VOR for descent - worked beautifully. Needless to say I never used this unapproved facility.

In answer to the question, I recollect that the answer is yes because we'd sometimes have one RMI tuned to the approach NDB and the other tuned to the g/a NDB. I don't have a MEL to hand to see if the majors for whom I flew permitted an NDB approach with one receiver u/s.

[keithl]

Without wishing to shine any spotlight where it might be unwelcome, there are many commercial aircraft around with only one ADF fitted (and no FMS). Most approaches can be managed with one, although the one Graybeard refers to is clearly an exception.
To answer the question - it is certainly legal.

[tired]

In all the countries I've flown in it's legal, provided the approach is not a 2 NDB approach - if it says "2 NDB" at the top of the Jepp plate then you need 2 separate ADFs in the aeroplane.

In my youth I did plenty of NDBs into dark African grass airfields at night with only 1 ADF on board, never seemed to be a problem then. But I was in regular practice in those days - don't think I'd have the skills and confidence now. The joys of shiny jets with expensive equipment! :hmm:

[Pugilistic Animus]

unless it says DME required on the plate:ugh:

[Anotherflapoperator]

Our old knackered 146 only has one ADF, mind you it also has a Trimble 2102 thing that isn't connected to the Autopilot either. The ADF needle is on the HSI, just an outer ring, though the needles are splitable if two ADF inputs were available. The twin VOR fit is on the DBI, an RMI indication of the other side's HSI heading.

Pretty crap really, how they call it BRNAV compliant is beyond me, but it is vintage 1984 and number 15 off the line. Things you fly for a few quid, eh?

Our home field has an NDB/DME approach avialable, but we rarely use it as there is also an ILS at both ends and radar control as well.

More importantly, our control unit allows a second NDB frequency to be pre-dialed and flipped with the switch if a Go-around were required at other airports.

Did I mention it's only CAT 1 as well.....not even good enough to be a water bomber....

[ShyTorque]

This boils down to the regulations regarding "minimum equipment for IFR" of the country in question.

For UK this is laid down in Schedule 5 of the ANO.

Relevant for approach phase is "Scale H".
[Quote]
(i) Subject to paragraph (ii), radio navigation equipment capable of enabling the aircraft to be navigated on the intended route including:
(a) automatic direction finding equipment;
(b) distance measuring equipment;
(c) duplicated VHF omni-range equipment; and
(d) a 75 MHz marker beacon receiver.

[212man]

Basil, haven't checked this thread for a while. What I meant was in the particular case referred to, that resulted in the loss of a 737: that approach did require two ADFs to be tuned to two NDBs, but the a/c only had one ADF.

[captainpaddy]

JAR OPS 1.865 says that you must have one VOR, one DME and one ADF as a minimum (except that you don't need an ADF if you won't be using one at any stage of your intended route).

Paragraph (c) part (v) then says that you need an additional ADF (to make two) when navigation is based solely on NDB signals. That would mean that for an NDB/DME you would need just one ADF and one DME (as DME is considered as a means of navigating) but for a pure NDB approach with no other navaid available, you need two ADF's.

[Capt Fathom]

that approach did require two ADFs to be tuned to two NDBs, but the a/c only had one ADF.

Not true in my part of the world. Twin NDB approach only requires one ADF. All that is required is at station passage, you tune the next NDB. Messy, but legal!

[Graybeard]

Not true in my part of the world. Twin NDB approach only requires one ADF. All that is required is at station passage, you tune the next NDB. Messy, but legal!
Legal, but stupid.

ADF receivers prior to the Arinc 700 series (767 and later) have zero redundant circuitry, and no feedback that the indication to the pilot matches the receiver's output. Disregarding all the operational factors, subjecting large airplanes and their contents to a single string of circuitry is foolhardy, and would not pass the simplest Fault Analysis.

It's a bit puzzling to me that dual VOR would be required, and not dual ADF.

GB

[galaxy flyer]

The AF 737 accident was indeed because of one on-board ADF receiver flying a two NDB approach. The two NDBs are "in-line" with one apx. 5 miles from the runway end and the other at the LMM position just short of the runway. That was a legal approach under early (50's) PANS-OPS standards, basically, the approach designer used two trapazoids-one expanding from the NDB on final, merging with a trapazoid narrowing toward the beacon just short of the runway. Absolutely requires two ADF receivers to legally fly. The point of the design was to allow lower mins due to the terrain "eliminated" from the design with two trapazoids. Also provides a positive MAP not using timing. I do not believe this is still a PANS-OPS approach design. Any comments??

GF

[LEM]

for a pure NDB approach with no other navaid available, you need two ADF's.

captainpaddy, if this is correct (and certainly is if you say so), then we have our answer.

Just one doubt remains: is that statement referring to dispatch or actually flying the approach?
(let's say you departed with 2 ADF, and later on one fails in cruise, then you have only one left for the approach...)

[Clandestino]

If there´s doubt, then there is no doubt.

If you fly solely by NDB, then you have to have two operative NDBs onboard. So if one fails inflight, you can´t do NDB alone approach. If there are no other approaches available, then you divert, unless PiC´s emergency authority is invoked.

Regarding T-43 crash at Dubrovnik, Croatia, there was excellent article about it by Peter Garrisson, in Flying magazine, some ten years ago. It was called "Minor deviations" and I guess it made it to one of his "Aftermath" books. To sum it up: weather was marginal, approach was not stabilized (they crossed FAF at 210kt), sole ADF remained tuned to KLP (FAF) and not CV (LMM), procedure designer calculated too low MDA. And mountain had PK 1.

[captainpaddy]

if one fails inflight, you can´t do NDB alone approach. If there are no other approaches available, then you divert, unless PiC´s emergency authority is invoked.

LEM,

I think Clandestino has got it. It's certainly how I understand it. I think the JAR OPS section I referred to would relate to all cases as it does not specifically mention dispatch. If you're enroute and one ADF fails you must look for an alternative such as a different approach at the same airport (perhaps a circle) or a diversion. Only Captains emergency authority would allow you to continue a NDB approach with one ADF. As with all uses of this authority, then you really need to be sure you have a good excuse!! :)

[captainpaddy]

You can read the relevant section here:

Click on JAR OPS 1 for the pdf.

http://www.jaa.nl/publications/section1.html

1.865