When to start descent from high altitude under lost comm
Posted by tommyboy11011@reddit | flying | View on Reddit | 45 comments
You are an airliner cruising at 35,000 on an airway. Your clearance limit is the destination airport. Conditions are IMC at cruise and IMC at destination. You are not flying a STAR. When do you begin your descent from cruise?
jimcarroll_cfi@reddit
First, an airliner having complete comms failure is a serious emergency. With that many redundancies built in, loss of comms is virtually impossible & if it were to happen, something is seriously wrong. So the squwak is 7700.
Second, at FL350, your travelling 400-500 nm/hour, which is at least 200 nm in 30 minutes. It’s very unlikely you’d be in IMC all that time, in which case when you enter VFR, you stay in VFR and land.
Either way, once you are squwaking 7700, use your best judgement. ATC can see you, and will vector others out of your way. They expect you to use your best judgement (AIM 6-4-1 (Two-way Radio Communications Failure), paragraph (a)).
tommyboy11011@reddit (OP)
I appreciate your input and I am playing devil's advocate on this. But why would the FAA go out of their way to create a reg 91.185 describing how they want you to handle a descent in lost comm just for a pilot to ignore it and descend against what the reg says? Another website I was reading said lost comm should only be considered an emergency if you lose your ability to navigate or you are low on fuel.
jimcarroll_cfi@reddit
You are making complete sense — and your read of 91.185 is 100% correct — it’s just out of date. Those rules were written for a land before time. When radar coverage was spotty and pilots needed to submit position reports so ATC could mentally keep track if where we were.
In an age of Jet travel, with virtually 100% coverage afforded by ADS-B, those days are over. They can see us everywhere & even submit landing fees to unattended airports I land at 😫. On a checkride, your answer is the one to start with — but for sure, the dpe will follow up with SBT and probe — is that really what you’d do?
Its then you need to ask yourself. A modern airliner is a datacenter in the sky, with radio and satellite communication stystems (not to mention whatever hand held transceivers might be available). How much must have gone wrong with that plane to cause a comms blackout — and what is going to fail next?
Of course, maybe the trouble is with tracon or center. But at 7 miles above the earth, the plane can easily reach other controllers in their line of sight. Failing that, they pick up the sat phone and call dispatch who can relay the call over land lines.
Just saying — sure, know the regs and be ready to repeat them. But be more ready to apply real world actions.
jimcarroll_cfi@reddit
First, an airliner having complete comms failure is a serious emergency. With that many redundancies built in, loss of comms is virtually impossible & if it were to happen, something is seriously wrong. So the squwak is 7700.
Second, at FL350, your travelling 400-500 nm/hour, which is at least 200 nm in 30 minutes. It’s very unlikely you’d be in IMC all that time, in which case when you enter VFR, you stay in VFR and land.
Either way, once you are squwaking 7700, use your best judgement. ATC can see you, and will vector others out of your way. They expect you to use your best judgement (AIM 6-4-1 (Two-way Radio Communications Failure), paragraph (a)).
Tisx@reddit
(91.185 Paragraph 3 sub ii)
(ii) If the clearance limit is not a fix from which an approach begins, leave the clearance limit at the expect-further-clearance time if one has been received, or if none has been received, upon arrival over the clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and approach as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC) estimated time en route.
mflboys@reddit
Yeah this is the literal reading of the book answer. Overfly the airport, then direct to an IAF. Enter hold and begin descent from FL350 at the ETA. I guess you would descend in hold then proceed on the approach once at a normal altitude.
Real world, we’re expecting you to begin descent at your normal TOD, proceed to an IAF at a reasonable distance (maybe 50 NM), and execute the approach.
tommyboy11011@reddit (OP)
Are you a controller?
mflboys@reddit
Yes at a center.
tommyboy11011@reddit (OP)
Thanks for the input
mflboys@reddit
And for some more historical context on the “when to begin descent” part, which corroborates the reading that descent should begin at the IAF, here’s the Civil Air Regulation §60.49 from 1962:
So, the original language which has been gradually morphed and amended into the current reg did more clearly specify that descent begins at the approach fix.
tommyboy11011@reddit (OP)
Does ATC declare an emergency on behalf of the pilot under this situation?
mflboys@reddit
If we think an air carrier will be NORDO from cruise all the way to landing in IMC, an emergency would almost certainly be declared.
However, it isn’t a situation which triggers an automatic emergency declaration, such as simultaneous loss of radar and voice contact.
TK3K216@reddit
I could be wrong but I don’t know if the “overfly the airport” portion was ever meant to be that. Yes it’s the clearance limit but how do you overfly an airport if an airport isn’t a fix? From what I understand this was written well before GPS became a mainstream thing in aviation. Without GPS you can’t necessarily overfly an airport unless you’ve got a VOR or other nav aid directly over the field.
Did ATC maybe issue clearances differently back then in a way the literal wording makes more sense?
Not disagreeing with you in any way btw, I just don’t know why they don’t update the wording to make more sense.
mflboys@reddit
Yeah I agree that’s definitely not the original intent, but it’s how it must be interpreted in the context of modern operations.
Unfortunately, I’m not familiar enough with how things worked back then to know exactly what would’ve been happening. I’m under the impression that in the old nonradar ops, arrivals into a TRACON were placed into a holding stack above the TRACON airspace, and they would clear aircraft into their airspace from that holding stack one at a time. So most likely the “clearance limit” they were referencing was a holding pattern fix somewhere, not the destination airport.
BelmontRef@reddit
The R in TRACON is Radar. No radar, no TRACON. There used to be non-radar approach facilities but they weren’t TRACONs.
tommyboy11011@reddit (OP)
So you would wait to descend from high altitude until on the approach?
cephalopod11@reddit
Yes, you descend in the hold.
Pilot0160@reddit
If I’m flying something capable of FL350 then I have 2, usually 3 VHF radios, at least 1 HF radio, and possibly a satphone plus WiFi. If I can’t communicate at all it’s an emergency and I do whatever I need to do under my emergency authority
tommyboy11011@reddit (OP)
Lost comm by itself is NOT an emergency.
Pilot0160@reddit
That’s for the PIC to decide and if I have as many communication methods as I do on my jet and I lose comms, it IS an emergency.
3 VHF, 2 HF, SAT phone, starlink. If all those fail then something is very wrong
tommyboy11011@reddit (OP)
Yes it’s up to the pilot. I’m just pointing out it’s not by itself to be considered an emergency by the FAA. Your actions are always scrutinized of course.
Pilot0160@reddit
The FAA never decides what is or is not an emergency
tommyboy11011@reddit (OP)
This entire post is a thought exercise that shows a way of doing things on both sides of the coin as possibly valid. However the FAA can decide what is an emergency as evidenced by a control tower declaring an emergency for a flight.
spacecadet2399@reddit
What are you asking this for? As an airline pilot, I would consider lost comms in IMC an emergency. We're carrying passengers here; it's not just a pilot or two up there. And an emergency makes it a lot easier to justify our using 91.3 to do whatever we deem necessary to ensure safety of flight.
Also, think about the assumptions behind your question. It's IMC at FL350 and still IMC all the way to the ground. What kinds of weather can cause that? What kinds of weather do you think that flight is in when it loses comms? Yes, that is absolutely an emergency.
tommyboy11011@reddit (OP)
Let me change the scenario. You’re a turboprop at 250. No fms, wifi, sat phones. Just 2 comm radios. I radio is Mel. You have vor/loc needles only.
It’s a thought exercise. The letter of the law per the reg describes the list comm procedure which from what I can see says you circle down on the approach.
hhjijnnm@reddit
Keep it simple. I’m going to start a 2.5 degree descent angle to hit 10,000 feet AGL 30 miles out from the airport. Then slowly chop down as we prepare and self vector for the approach depending on traffic
Huge_Analysis_1298@reddit
Why 2.5 and not 3? 3 math is much simpler
hhjijnnm@reddit
2.5 is more chill and comfortable for passengers. No math needed I just type 2.5 and put it in :)
mflboys@reddit
And for some more historical context on the “when to begin descent” part, which corroborates the reading that descent should begin at the IAF, here’s the Civil Air Regulation §60.49 from 1962:
So, the original language which has been gradually morphed and amended into the current reg did more clearly specify that descent begins at the approach fix.
Herkdrvr@reddit
See 91.185.
tommyboy11011@reddit (OP)
I’m familiar with, but when would you leave 35,000
Lost_Cockroach6702@reddit
When your descent math makes sense for the IAF of the approach you are choosing to fly.
tommyboy11011@reddit (OP)
Can’t find where it says that
Lost_Cockroach6702@reddit
My answer is what you should actually do. If you start randomly holding in busy airspace then ATC is going to have an aneurysm. Controllers want you to squawk, follow the flight plan, land ASAP.
Law-of-Poe@reddit
Wouldn’t you commence your descent to arrive at the destination airport as close as possible to the filed arrival time?
tommyboy11011@reddit (OP)
I don’t know. I don’t think the reg says that?
Jzerious@reddit
Please correct me if I’m wrong. You are cleared to an airport but your clearance limit would be a fix or an Initial Approach Fix. In that case you would then start your approach from the IAF as close to your ETA time as practical
mflboys@reddit
Your clearance is limit the XXX in the “Cleared to XXX via . . .” portion of your clearance, which 99.99% of the time is your destination airport.
tommyboy11011@reddit (OP)
When you are cleared to an airport your clearance limit is the airport. From the airport you proceed to an IAF on a segment or maybe MSA altitude or higher. When you start down from 35,000 though?
z0mbeh8r@reddit
I’m going to do things as close to their normal time as possible and perform a normal descent to the airport. 3 nm per 1000’ feet of altitude I need to lose plus a 10% fudge factor for speed reductions and configuration changes.
tommyboy11011@reddit (OP)
Do you interpret 91.185 to begin the approach as close to the ETA as possible at published altitude on approach chart or descend in the hold on the ILS from cruise altitude? Looking for the real rule as written. Thx
z0mbeh8r@reddit
I’m using 91.3(b). I have 3 VHF radios, and typically at least 1, sometimes 2 HF radios and maybe even satcom depending on the tail I’m flying that day. All powered from different electrical sources/busses. If I can’t communicate with anyone then something has gone very wrong. If I’m far enough away from my destination I will most likely not even attempt to continue there. If my destination was questionable for some reason, maybe not great RCC with active winter time precipitation or last weather required a CAT 2 or 3 ILS, I’m going somewhere else where I know the weather was better. 91.185 is a great way to start. But nothing in 91.185 says I can’t exercise PIC emergency authority. So I’ll do what I deem is safest, I won’t prolong our exposure to a bad situation and I’ll transmit everything we’re doing in the blind on both an appropriate ATC frequency and guard.
randombrain@reddit
If you're in anything that's capable of FL350 and not one of your multitude of radios and CPDLC and ACARS and satphone work, I think you're firmly in "this is an emergency" territory and you can do whatever you think makes sense.
tommyboy11011@reddit (OP)
We used to squawk 7700 for one minute and 7600 for 15 minutes and repeat. But we don’t do that anymore so not an emergency
rFlyingTower@reddit
This is a copy of the original post body for posterity:
You are an airliner cruising at 35,000 on an airway. Your clearance limit is the destination airport. Conditions are IMC at cruise and IMC at destination. You are not flying a STAR. When do you begin your descent from cruise?
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