How serious is failure to read-back hold-short or line-up instructions given by AC?

Does an ATC have a right to be upset if a pilot forgets to repeat these instructions?

Best Answer:

Linda.767: You fail the acknowledge safety instructions?
It is SERIOUS.
And fail to observe proper procedures.
Do I have to initiate $2,500 worth of fuel to do a go-around when you approach the runways?
Just "in case you forgot" to read back "hold short of the runway?"

Other answer:

Linda.767:
I can almost guarantee that if a pilot forgets to read back hold short instructions on a busy ATC ground/tower frequency, said pilot will experience ear pain in his headsets from the controller impatiently REPEATING his instructions. If you don't read back, the controller MUST repeat him/herself before the clearance is valid, and this takes up time on the frequency and can cause delays for everyone else. (Not to mention, can lead to accidents like the one FlagMichael describes. Pilots at busy terminals are expected to be on the ball and get it right the first time. If a student pilot or private pilot at a less busy controlled airport forgets to read back, ATC will still repeatr the instructions, but might be a little more patient and not roast the pilot over the air.
FlagMichael:
Very, very serious.

I work in the electric industry, where we use "three way communication" (read back) for switching procedures. A few years ago a sub tech was performing a switching procedure in a 500KV substation; both he and the dispatcher failed to notice they had missed a step and it triggered the biggest blackout in California history. A simple failure of read back was at the heart of the incident.

The equivalent of that sort of misunderstanding in aviation can result in loss of hundreds of lives. The worst airline accident in history was in large part caused by miscommunication, including failure to read back exactly as read – see the source. 583 people died. That sounds serious to me.

There is no room for carelessness in aviation. My brother, normally a very careful private pilot, was struck and knocked out by his own Cessna 140. He wanted to fly but his battery was dead, so he propped the engine. There were three careless problems: the throttle was open too far, the parking brake was not set, and it was not tied down. Fortunately, the fuel truck the runaway plane ran into was empty. If failure to read back does not give you cold sweat, you are not taking flying seriously enough.

Kyle:
Very serious. We can and WILL be screaming at you if you a) DON'T read back a hold-short instruction and b) pull onto the runway without a clearance. Depending on the severity of the situation, we have the right and the responsibility to report you to FSDO, who will then decide what course of action to take.

TL:DR, if ATC gives you a hold-short clearance, read it back,

Skipper747:
If you collide your C-152 with a 747 with 500+ passengers…
And the 747 crashes…
I think ATC (and FAA) might be ("somewhat") upset about your superior airmanship –
Yes they have the right… and the FAA even has the right to suspend your pilot certificate too…
It is called "failure to observe proper radio-communication procedures" –

In some countries, you might even go to jail…

Warbird Pilot:
He needs to hear it to know communication was effective.