Sometimes I have nightmares about getting confused in the cockpit and doing something so foolish that pilots all over the world will slap their foreheads in wonder. This is that kind of foolish. There may be snark ahead.

The Air Accident Investigation Unit (AAIU) of Ireland released a report on a serious incident which at its heart is simply a bit of RT gone wrong.

The aircraft was a BAe 125-800B (Hawker) twin-engine corporate jet, registration N1310H. The flight crew and two passengers filed an IFR flight plan from Kerry Airport in Ireland to Gander, Newfoundland in Canada.

We’ll focus on the radio calls for this one.

While the aircraft was taxying to the runway, the Kerry Airport Tower controller gave the flight crew their full oceanic clearance; however there seemed to be something wrong in the aircraft, as he had to ask them to read back the clearance three times. This was resolved after one of the flight crew said they were trying another mic, was it any better? It was and there were no further issues understanding the transmissions.

The Tower controller contacted Shannon Low Level (Planning) Control by phone and asked if he could have “a climb out for him off Two Six please…if I can get on track to VENER it would be fantastic.” This is standard, allowing the aircraft a more direct routing for the first stage of the flight. The controller was pretty sure Shannon would approve it.

The Shannon Low Level Data Assistant responded “Okay Kerry, November One Three One Zero Hotel is cleared from Kerry to Gander via VENER, Flight Level Three Four Zero, squawk Six Three Zero Four and on track to stop at Flight Level Two Zero Zero”

The squawk is an instruction of the identifying code that the flight crew should enter into their transponder. In this case, they will key in 6304 which the transponder will transmit. Controllers in the area with secondary surveillance radar (i.e. Shannon) will see the radar track with this identifying number and the aircraft’s altitude. It’s an easy way of knowing which plane is which.

The important part of this clearance is that the aircraft has been cleared to fly direct to the waypoint VENER on the way to Gander, with an initial clearance to Flight Level Two Zero Zero: FL200.

Flight levels are given in hundreds of feet based on a standardised pressure; which means they are not necessarily the same as the aircraft’s true altitude. This allows for for all aircraft operating on flight levels to be calibrated to the same defined altitude, regardless of the actual pressure. It’s specifically used after transition altitude; until then, the true altitude of your aircraft in respect of the ground is more important.

In the US and Canada, the transition altitude is 18,000 feet, so the transition level is FL180. In New Zealand, it is FL130. In Europe, it varies and can be as low as 3,000 feet, or FL30.

At Kerry Airport, the transition level is FL050, or 5,000 feet.

Kerry Tower Controller: One Three One Zero Hotel *you’re cleared on track to VENER stop climb Flight Level Two Hundred* squawk Six Three Zero Four Flight Crew: “Okay *cleared direct to VENER climb maintain Flight Level Two Hundred* and squawking Six Three Zero Four in the meter back taxiing for Two Six One Zero Hotel Kerry Tower Controller: “One Zero Hotel read back correct report ready for departure”

The emphasis is mine to focus on the instruction that the controller gave and that the flight crew read back: the aircraft is cleared to fly direct to the waypoint called VENER and to climb to FL200.

Now everyone including my non-flying readers should be clear by now that FL200 is 20,000 feet. This is pretty basic. 2,000 feet is lower than the transition level everywhere in the world and there’s no corporate jet that can fly at 200,000 feet, so even if you are a bit taken aback by all those zeroes, you’d work out that the clearance must be to 20,000 feet.

Of course, one expects a pilot to know such things anyway.

The BAe125 took off and changed frequency to Shannon Low Level Control and confirmed the clearance that they’d been given.

When you take off from Kerry, you can see the Slieve Mish mountains in the distance. The Minimum Sector Altitude (MSA) is 4,500 feet (1,370 metres), which is the lowest altitude which will provide a minimum clearance of 1,000 feet (300 metres) above all objects in the sector. The aircraft climbed to 2,000 feet (610 metres) and then levelled off in cloud, heading straight for the mountains.

Flight Crew: Shanwick, good afternoon, Hawker November One Three One Zero Hotel Flight Level Two Zero Zero direct VENER Shannon Low Level Control: November One Three One Zero Hotel Shannon control confirm squawk and passing altitude”

This is a standard request to confirm the code that you are broadcasting on the transponder and the altitude level that you are climbing through, as obviously during the climb you are not at a single altitude.

As the transition altitude is 5,000 feet at Kerry Airport, the passing altitude would be given in feet based on the current pressure if under 5,000 feet and as a flight level if over 5,000 feet, say FL050 if at the transition level.

Flight Crew: Ah we are level Flight Level Two Zero Zero and squawking Six Three Zero Four

The controller stared at his display. The squawk was correct but the displayed altitude didn’t seem to be. The aircraft was not showing as at FL200 but closer 2,000 feet. He knew that Kerry is surrounded by high ground and checked his charts: the rising terrain in the aircraft’s path was 2,800 feet.

Shannon Low Level Control: November One Three One Zero Hotel Shannon radar contact and just confirm your passing altitude. Flight Crew: We were cleared only to Flight Level Two Zero Zero Shannon Low Level Control: “Okay sir that’s copied but your passing altitude…your current altitude

That’s now the third time he’s asked. The incident report actually uses the term persisted to describe the controller’s question. He does not want to hear the clearance, he wants the flight crew to confirm, right now, what their current altitude is. Note the use of the term altitude rather than level, because the flight levels don’t start until FL050.

Flight Crew: And we confirm that we are cleared up to Flight Level Zero Two Zero… Two Thousand feet

Note that the crew member now says Zero Two Zero for their current altitude, the first sign of the confusion in the cockpit. They have levelled off at 2,000 feet.

The Tower Controller at Kerry had listened in on the Shannon frequency; because of the mountains, he could only hear the aircraft and not the controller. He knew, he said, as soon as he heard the flight crew reporting “level” that something was wrong. He phoned Shannon Low Level and was speaking to the assistant when the Shannon Controller rang him directly.

Shannon: Can you see that [aircraft]? Kerry: I can still see him, yeah. He’s going through cloud there now. He was cleared to Flight Level Two Zero Zero. Shannon: “I know. He stopped at Two Thousand and the Mish Mountains are there at Two Thousand Eight Hundred. Is he above them can you see? Kerry: He’s just gone into cloud there now.

Shannon Low Level Control: November One Three One Zero Hotel, Negative. Climb Flight Level Three Zero Zero Flight Crew: Flight Level Three Zero Zero

Negative, as in, No! You are not cleared to two thousand feet. Climb! According to the Belfast Telegraph, they were only within a minute’s flight of the highest peak of the mountains.

(If you are wondering why the new flight level, coincidentally, Shannon High Level had just put forward that the aircraft could climb up into their airspace at FL300.)

Under the circumstances, the controller’s call is not great, it has to be said. If they don’t know what FL200 is, what’s the odds they are going to climb to 3,000 feet and level out again? I think this must have occurred to the controller at the same moment.

Shannon Low Level Control: And November One Three One Zero Hotel, you can caution high ground…If you can expedite your climb till flight till correction …through Four Thousand feet

Through four thousand feet means don’t level off at four thousand, do not stop climbing, just get up there!

Poor controller.

Flight Crew: Expediting through up to Flight Level Three Zero Zero

Once they were out of danger, the controller called again.

Shannon Low Level Control: Okay I just want to confirm with you your cleared Flight Level initially which you were given by Kerry…your climb out instruction.. was that to Two Thousand feet or to Flight Level Two Zero Zero. Flight Crew: We read back Flight Level Zero Two Zero… Two Thousand feet Shannon Low Level Control: Okay, that’s copied thank you, Kerry seem to think that they gave you Flight Level …ah… Two Zero Zero so we might have to report that just to let you know. Flight Crew: Okay.

You were there with me, right? They did not read back Flight Level Zero Two Zero! Never mind that that is a flight level that doesn’t exist. The exchange was recorded, of course, which is why we know exactly who said what. Still.

The Pilot in Command of the aircraft was contacted after the flight and asked to report what had happened.

Our altitude climb instruction was “climb level Two Hundred”. We read back the clearance and began the departure. As we began to climb we had some confusion as to what the altitude clearance limit was as we were unsure what level Two Hundred meant. We levelled at Two Thousand feet to ensure we didn’t exceed any altitude limits. We contacted departure control and informed them we were level, they questioned what altitude we were climbing through and we clarified that we were level. There was some question from ATC regarding what altitude we were cleared up to by Kerry and we informed the controller that we were unsure but were level at Two Thousand. He further cleared us to Flight Level Three Zero Zero and to expedite through Four Thousand Five Hundred, and we immediately began climbing. The flight continued on without incident.

Now, I’m not usually one to harp on about mistakes. I still get my left and right confused when under pressure and I’ve even said “South” when I meant “North”. It happens.

And there’s the difference in how the transition level is handled. The flight crew was American and were used to a transition at 18,000 feet. Clearly, they were aware that the transition levels are much lower than they are used to, so it might be easy to get confused.

My problem here is this:

As we began to climb we had some confusion as to what the altitude clearance limit was as we were unsure what level Two Hundred meant.

FL200 is the same in the US as it is in Ireland and everywhere else in the world. It never, ever, anywhere means 2,000 feet.

I suspect here he’s making the point that in the US (and pretty much everywhere outside of the UK and Ireland), the correct phraseology is Flight Level Two Zero Zero, not Two Hundred. The UK CAA and some other European agencies advocate using hundreds when assigning a flight level clearance which ends in two zeros.

However, the flight crew repeated the clearance back as Two Hundred without issue and in other contexts used group numbers (Five Zero as Fifty and One Two Four decimal Seven as One Twenty Four decimal Seven), so they seem to have been comfortable working with grouped digits.

In any event, on the later calls the flight crew is quite adamant that they were cleared to Flight Level Two Zero Zero, so they clearly understood the original Flight Level Two Hundred to mean FL200.

So the only confusion is the correct level to fly when cleared to FL200. And honestly, if they weren’t sure? Then bloody ask.

Instead, they totally arbitrarily decided to level off at 2,000, disregarding the local terrain completely, in order to ensure they didn’t exceed any altitude limits.

They did not inform the controller that they were unsure, in fact, they quietly just carried on and did not clarify the issue until the controller insisted. And when he did, they claimed that they were given the wrong flight level.

The investigation analysis concludes that the flight crew never referred to being unsure of when they should stop climbing and they never questioned the various statements of the controllers or requested clarification. The report notes that the flight crew may have first realised there was a problem when they transmitted that they were cleared up to level Zero Two Zero for the first time, that is, after the controller had asked three times.

In fact, it appears that it was only following three direct inquiries in quick succession from Shannon Low Level Control that the crew identified that they were confused about their cleared level. When the Shannon Low Level Control enquired for a third time the Flight Crew reported “And we confirm that we are cleared up to Flight Level Zero Two Zero… Two Thousand feet”. This was a change from the Flight Crew’s two initial reports that they were level at “Flight Level Two Zero Zero” and probably reflects a realisation of their behalf that they had correctly heard and recorded “Flight Level Two Hundred/Flight Level Two Zero Zero”, but that they had misinterpreted its meaning. This is supported by the fact that the Flight Crew did not at any stage request a clarification of their cleared Flight Level which, if they were confused or concerned, would be good airmanship and is the practice advocated by Eurocontrol.

Probable cause:

1. The aircraft levelled at Two Thousand feet in close proximity to mountainous terrain, contrary to ATC clearance.

Contributory Causes:

1. The Flight Crew misinterpreted Flight Level Two Hundred as Two Thousand feet.

2. Clarification was not sought from ATC regarding the assigned stop climb Flight Level.

I am pretty quick to admit my bias: it’s not often I get upset at pilots for making a mistake.

But this isn’t about a momentary cock-up. It’s about clarifying instructions to make sure you know what you are doing and it’s about acknowledging when you have made a mistake.

I guess the main thing is, they climbed away from those mountains (obscured by cloud!) before it was too late. More luck than good management, in my opinion.

Edit: I have just realised that the original accident report wasn’t included in this; sorry about that! You can read it on the AAIU site here: http://www.aaiu.ie/node/907.